Cytoskeletal Strain Amplification due to Bone Fluid Flow

描述(申请人提供)：骨骼很容易适应它的机械 加载环境。人们普遍认为，这种适应的“机械传感器” 成为骨细胞，尽管实际的过程是未知的，并且对 了解新骨形成的过程。然而，有一个正在出现的 一致认为应变诱导的间质流体流动在这一过程中起关键作用 机械信号。在这项提案中，我们解决了一个新问题： 骨细胞对液体流动的“感觉”受存在的一种 具有连接细胞突起的横向细丝的细胞周基质 并将流体动力阻力传递到系绳上 细胞突起中的细丝到细胞内的肌动蛋白细胞骨架？我们的 初步研究已经揭示了这种横向的第一个明确的识别 桥接光纤和一种新的理论模型(You等人，2001) 为定量探索这一假说而发展起来的。此模型使 值得注意的预测是，活骨中非常小的机械应变可以 在细胞水平上被放大100倍。如果经过验证，该模型将解析 根本的悖论。这解释了为什么整个骨骼的组织水平应变可以 比体外测量的动态底物应变小得多 以引起细胞内的生化反应。在建议的研究中，我们会 通过实验验证和测量所需的基本生物元素 这个新型号。具体地说，我们将：(1)表征间距和 将细胞突起连接到细胞突起的横向元件的分布 (2)用免疫组织化学染色技术鉴定， 填充细胞周隙的蛋白多糖；(3)阐明结构 充满细胞突起的肌动蛋白细丝束；以及(4)提纯 预测细胞水平应变放大的理论模型 由于流体对细胞周围基质的拖曳，在细胞过程中发生。

DESCRIPTION (provided by applicant): Bone adapts readily to its mechanical loading environment. The "mechanosensor" for this adaptation is widely believed to be the osteocyte, though the actual process is both unknown and critical to understanding the process of new bone formation. However, there is an emerging consensus that strain-induced interstitial fluid flow plays a key role in this mechanical signaling. In this proposal we address a new question: How would the osteocyte "perception" of fluid flow be influenced by the presence of a pericellular matrix with transverse filaments that both tether the cell process to the canalicular wall and transmit fluid dynamic drag forces on the tethering filaments to the intracellular actin cytoskeleton in the cell processes? Our pilot studies have revealed the first clear identification of such transverse bridging fibers and a new theoretical model (You et al., 2001) has been developed to quantitatively explore this hypothesis. This model makes the remarkable prediction that the very small mechanical strains in live bone can be amplified 100-fold at the cellular level. If validated, the model resolves a fundamental paradox. It explains why tissue level strains in whole bone can be so much smaller than that measured in vitro dynamic substrate strains required to elicit intracellular biochemical responses. In the proposed studies, we will experimentally verify and measure the essential biological elements required by this new model. In particular, we will: (1) characterize the spacing and distribution of the transverse elements that tether the cell process to the canalicular wall; (2) identify, using immunohistochemical staining techniques, the proteoglycans that fill the pericellular space; (3) elucidate the structure of the actin filament bundle that fills the cell process; and (4) refine the theoretical model for predicting the cellular level strain amplification that occurs in the cell process due to the fluid drag on the pericellular matrix.