Structural, Molecular, and Functional Specialization in Osteocyte Mechanosensing

描述（由申请人提供）：骨细胞，存在于骨基质中的细胞，是最丰富的骨细胞。它们在骨中起机械传感器的作用，对激活和协调破骨细胞和成骨细胞的活动至关重要，通过这些活动，骨适应机械使用，保持其健康并防止骨折。骨细胞机械转导的机制尚不清楚，尽管骨细胞机械敏感性的变化与骨合成代谢剂和性激素的调节作用有关。我们已经开发了工程模型，表明小的整个骨应变可以通过局部附着在骨管壁的骨细胞过程周围局部放大。骨细胞细胞体不能看到类似的高应变，因为它们太柔顺，缺乏局部应变扩增所需的细胞附着物。这些数学模型认为，骨细胞过程可能是独特设计的功能作为一个检测器的小组织菌株。为了验证这一假设，我们开发了一个基础广泛的多pi程序，结合了离子通道生理学、体内骨细胞结构/生物力学和生物工程/建模方面的专业知识，以了解骨细胞如何感知和转导其局部机械环境。该项目将a)利用培养骨细胞的电生理学方法检查骨细胞机械反应的功能极性（目标1），b)鉴定骨细胞机械转导复合物的分子成分（目标2），c)表征体内骨细胞的机械转导复合物的结构（目标3）和d)建立将骨细胞过程和细胞体的局部水动力和膜张力与体外和体内细胞反应联系起来的综合数学模型（目标4）。我们还开发了一种新技术（“Stokesian”流体刺激探针），使我们能够在极低的力（<10pN）下对骨细胞过程和细胞体进行流体动力加载，这是骨细胞在体内实际经历的典型力。扩大这项技术，在广泛的细胞类型中询问机械反应性是这项资助的发展目标。意义：了解骨细胞如何“感知”和转导机械信号可能为骨生理学提供关键的新见解，从而发现对抗衰老和疾病导致的骨质流失的新治疗靶点。

DESCRIPTION (provided by applicant): Osteocytes, the cells that reside within bone matrix, are the most abundant bone cells. They function as the mechanical sensors in bone, and are critical to activation and coordination of osteoclastic and osteoblastic activities by which bone adapts to mechanical usage, maintains its health and prevents fractures. The mechanisms underlying osteocyte mechanotransduction are not well understood, though changes osteocyte mechanosensitivity have been implicated in regulating the effect of both bone anabolic agents and sex hormones. We have developed engineering models which show that small whole bone strains can be amplified locally around osteocyte processes by focal attachments to the canalicular wall. Osteocyte cell bodies cannot see similar high strains as they are too compliant and lack the cellular attachments needed for local strain amplification. These mathematical models argue that the osteocyte cell process may be uniquely designed to function as a detector of small tissue strains. To test this hypothesis, we developed a broad-based multiple-PI program that combines expertise in ion channel physiology, in vivo osteocyte structure/biomechanics and bioengineering/modeling to understand how osteocytes perceive and transduce their local mechanical environment. This program will a) examine the functional polarity of osteocyte mechano- responsiveness using electrophysiological approaches on cultured osteocytes (Aim 1), b) identify the molecular components of mechanotransduction complexes in osteocytes (Aim 2), c) characterize the structure of the mechanotransduction complex in osteocytes in vivo (Aim 3) and d) build integrative mathematical models relating local hydrodynamic forces and membrane strains at osteocyte processes and cell bodies to cellular responses in vitro and in vivo (Aim 4). We have also developed a novel technology ("Stokesian" Fluid Stimulus probe) that allows us to hydrodynamically load osteocyte processes vs. cell bodies at extremely low forces (<10pN) typical of what bone cells actually experience in vivo. Expansion of this technology to interrogate mechano-responsiveness in a broad range of cell types is a developmental goal of this grant. Significance: Understanding how osteocytes "perceive" and transduce mechanical signals may provide key new insights into bone physiology leading to the identification of novel therapeutic targets against bone loss due to aging and disease.