Brief Rest-Intervals Amplify the Response of Bone to Mechanical Loading

描述(申请人提供)：该项目的总体目标是优化零负荷休息间隔的能力，以极大地放大骨骼对机械负荷的响应。我们在美国国立卫生研究院以前资助的一个项目中发现并开发了这一新的标准循环载荷修改。我们的数据表明，每个负荷周期之间的短暂休息间隔有助于降低启动骨膜骨形成所需的应变大小，并减少骨对重复机械负荷的适应。在这个项目中，我们假设休息插入负荷的成骨效益是可以优化的，因为与重复的循环负荷相比，短暂的休息间隔显著地增强和维持了钙/NFAT介导的基因和蛋白质调节。为了探索这一普遍假设，我们将使用一种综合的多学科方法(体内机械加载、RT-PCR、免疫组织化学、组织形态计量学和一种新的基于硅胶剂的骨细胞动力学模型)来追求三个S目标。在这些S.目标中，我们将：1)定义最大限度地促进骨膜骨形成的休息间隔时间、加载天数和循环次数的最佳组合，2)定义单次和多轮休息插入或循环加载后骨细胞基因调控的急性变化，以及3)执行一系列体内验证实验，最终尝试使用优化的休息插入加载干预来将骨膜骨形成靶向于我们体内模型中的新的皮质部位。如果我们能够充分了解静息插入负荷的潜在信号通路，从而能够优化和靶向局部骨膜骨形成，我们相信接下来将适合在人类身上启动临床试验来测试这一策略。从生物学的角度来看，我们相信拟议的研究将揭示机械转导通路的新见解，通过这些途径，休息插入负荷获得其实质性的好处。与公共健康相关：该项目专注于通过实验优化和机械探索细胞信号通路，这些信号通路是零负荷休息间歇在增强骨骼对机械负荷的反应方面令人惊讶的有效性背后的基础。从临床角度来看，该项目的成功将提高将这一概念转化为治疗骨丢失病理的非侵入性、非药物干预的可能性。

DESCRIPTION (provided by applicant): The broad goal of this project is to optimize the ability of zero load rest-intervals to greatly magnify the response of bone to mechanical loading. We identified and developed this novel modification of standard cyclic loading during a previous NIH funded project. Our data indicate that brief rest-intervals between each load cycle serve to lower the magnitude of strain required to initiate periosteal bone formation and diminish the accommodation of bone to repetitive bouts of mechanical loading. In this project, we hypothesize that the osteogenic benefit of rest-inserted loading can be optimized because brief rest-intervals acutely enhance and sustain Ca2+/NFAT mediated gene and protein regulation compared with repetitive cyclic loading. To explore this general hypothesis, we will use an integrated multi-disciplinary approach (in vivo mechanical loading, RT- PCR, immunohistochemistry, histomorphometry, and a novel in silica agent based model of bone cell dynamics) to pursue three S. Aims. In these S. Aims, we will: 1) define an optimal combination of rest-interval duration, days of loading, and cycle number that will maximally enhance periosteal bone formation, 2) define acute alterations in bone cell gene regulation following single bout and multiple bouts of rest-inserted or cyclic loading, and 3) perform a series of in vivo validation experiments that will culminate with an attempt to use an optimized rest-inserted loading intervention to target periosteal bone formation to novel cortical sites in our in vivo model. If we are able to sufficiently understand the underlying signaling pathways of rest-inserted loading such that we are able to optimize and target focal periosteal bone formation, we believe it would then be appropriate to initiate a clinical trial to test this strategy in humans. From a biological perspective, we believe the proposed studies will reveal new insights into the mechanotransduction pathways by which rest-inserted loading derives its substantial benefits. PUBLIC HEALTH RELEVANCE: This project is focused on experimentally optimizing and mechanistically exploring the cellular signaling pathways underlying the surprising effectiveness of zero load rest-intervals in enhancing the response of bone to mechanical loading. From a clinical perspective, success in this project would improve the potential to translate this concept into a non-invasive, non-pharmacologic intervention for bone loss pathologies.