Skeletal Response to Applied Mechanical Loads in the Mouse Tibia

骨骼的骨包含两种组织结构：（1）致密皮质骨，形成长骨的外壳和中心轴的高体积分数材料，和（2）低体积分数松质骨，位于骨的内部和末端的开放式网状结构。一般来说，这两种结构被简单地视为单一的材料，“骨”，而不是区分它们的个体特征。然而，松质骨和皮质骨有不同的发育途径，并适应不同的生物物理刺激，特别是机械负荷。施加在骨骼上的负荷是合成代谢的，增加骨量并逆转成人的骨质流失。这项工作的总体假设是，在体内加载驱动定量基因表达不同的皮质骨和松质骨，导致不同的年龄和位置的机械负荷的反应。这项研究有可能通过识别刺激骨形成的遗传靶点来造福社会，这对衰老和骨质疏松症和关节置换等肌肉骨骼疾病至关重要。尽管这些方法已经彻底改变了其他领域，但还没有以组织-骨包膜-骨特异性的方式分析骨中的基因表达。 作为这项研究的一个组成部分，首席研究员计划作出几项努力，以增加妇女对科学的参与。 具体来说，她将，（1）通过基于本研究的研讨会，让中学女生参与STEM学习;（2）让女学生参与她的研究实验室;以及，（3）努力增加康奈尔大学和全国学术界STEM部门的女教师人数。使用最先进的下一代基因测序技术，这项工作将确定骨骼分子机制，激活响应机械刺激。在第一个目标中，重点将分别放在松质骨和皮质骨组织中机械生物学骨形成的调节上。使用生长期和成年雌性小鼠胫骨的受控体内负荷，将使用分离小鼠胫骨近端组织的方法测定基因表达和蛋白质定位的变化。此后，将在皮质骨中研究载荷大小与组织反应之间的特定关系。本研究的目标是确定皮质内与生长中雌性小鼠胫骨骨干沿着轴向变化载荷大小相关的信号传导途径。这项工作将确定未来的目标，以抑制或刺激基因表达和/或包膜特异性信号传导机制，以提高体内骨形成。最终，这些结果可以允许以组织特异性方式在体内刺激骨量，以减少患有肌肉骨骼疾病的个体的痛苦和经济负担。

The bones of the skeleton contain two tissue structures: (1) dense cortical bone, a high volume fraction material forming the outer shell and central shafts of long bones, and, (2) low volume fraction cancellous bone, an open-­lattice structure located in the interior and ends of bones. In general, these two structures are treated simply as a single material, 'bone' rather than distinguishing their individual characteristics. However, cancellous and cortical bone have different developmental pathways and adapt differently to biophysical stimuli, particularly mechanical loading. Loads applied to the skeleton are anabolic, increasing bone mass and reversing bone loss in the adult. The overall hypothesis of this work is that in vivo loading drives quantitative gene expression differently in cortical and cancellous bone, leading to differential responses to mechanical loading with age and location. This research has potential to benefit society through the identification of genetic targets to stimulate bone formation, which is critical to aging and musculoskeletal conditions such as osteoporosis and joint replacement. Gene expression has not been analyzed in a tissue-­envelope-­specific manner in bone despite these approaches having revolutionized other fields. As an integral part of this research, the principal investigator plans several efforts to increase the participation of women in science. Specifically she will, (1) engage middle school girls in STEM learning via workshops based on this research; (2) involve female students in her research laboratory; and, (3) work to increase representation of women faculty in STEM departments in academia at Cornell and nationwide.Using state-­of-­the-­art next generation gene sequencing techniques, this work will identify skeletal molecular mechanisms that are activated in response to mechanical stimuli. In the first objective, the emphasis will be on the regulation of mechanobiologic bone formation in cancellous and cortical tissue separately. Using controlled in vivo loading of the tibia in growing and adult female mice, changes in gene expression and protein localization will be determined using methods to isolate the tissues in the mouse proximal tibia. Thereafter, the specific relationship between the magnitude of loading and the tissue response will be studied in cortical bone. Here the goal will be to identify signaling pathways within the cortex associated with axially-­varying load magnitude along the diaphysis of the tibia in growing female mice. This work will identify future targets to inhibit or stimulate gene expression and/or envelope-­specific signaling mechanisms to enhance bone formation in vivo. Ultimately these results may allow stimulation of bone mass in vivo in a tissue-­specific fashion to decrease suffering and economic burden in individuals with musculoskeletal disorders.