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

描述（由申请人提供）：本项目的总体目标是优化零载荷休息间隔的能力，以极大地放大骨对机械载荷的响应。在之前的NIH资助项目中，我们确定并开发了这种新的标准循环加载修改。我们的数据表明，每次载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载荷的适应性。在这个项目中，我们假设休息插入加载的成骨益处可以优化，因为与重复循环加载相比，短暂的休息间隔可以显著增强和维持Ca2+/NFAT介导的基因和蛋白质调控。为了探索这一普遍假设，我们将采用综合的多学科方法（体内机械负荷、RT- PCR、免疫组织化学、组织形态计量学和一种新的基于二氧化硅剂的骨细胞动力学模型）来实现三个目标。在这些目标中，我们将：1)确定最大限度地增强骨膜骨形成的休息间隔时间、加载天数和周期数的最佳组合；2)确定单次和多次休息插入或循环加载后骨细胞基因调控的急性改变；3)进行一系列体内验证实验，最终尝试在我们的体内模型中使用优化的rest-inserted（置入）loading干预将骨膜骨形成定位到新的皮质部位。如果我们能够充分了解rest-inserted loading的潜在信号通路，这样我们就能够优化和靶向局灶性骨膜骨形成，我们相信这将是合适的，然后启动临床试验来测试这一策略在人类。从生物学的角度来看，我们相信我们提出的研究将揭示新的机械转导途径，通过这些途径，静置插入载荷获得了实质性的好处。

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.