Osteocyte-independent mechanotransducation of interstitial fluid flow in bone

描述（由申请人提供）：大量证据表明，骨骼间质液流（IFF）介导了骨重建对机械负荷的反应。我们的长期目标是开发基于IFF的骨细胞机械转导的骨丢失治疗方法。实现这一目标的关键一步是了解暴露于IFF的骨细胞的反应如何导致骨重建。最近，Tatsumi及其同事建立了一种具有诱导性骨细胞消融的转基因小鼠模型。有趣的是，尽管这些小鼠在后肢悬吊时对骨丢失有抵抗力，但这些小鼠在重新加载时的机械转导是正常的。这就产生了一种有趣的可能性，即骨细胞调节IFF介导的骨丢失，而在重新加载期间IFF的增加可能通过直接刺激其他类型的骨细胞来诱导骨形成。我们的中心假设是，IFF介导的骨吸收和形成过程中发生的卸载和重装两种不同的机制。在卸载过程中，缺乏IFF导致骨细胞介导的骨吸收。在重新加载期间，增加的IFF通过直接刺激成骨细胞或其祖细胞诱导骨形成。最近，我们的实验室开发了一种新的微流控装置，用于在后肢悬吊小鼠股骨中产生动态IFF。该器械将用于确定骨细胞在天然组织环境中介导流动诱导的骨重建中的作用。具体来说，我们将首先在有和没有消融骨细胞的后肢悬吊小鼠中诱导IFF，以确定IFF在废用后抑制骨细胞活性的能力，以及骨细胞在介导这一过程中的作用（目的1）。接下来，通过在骨细胞消融前施加一段时间的后肢悬浮，我们将确定IFF刺激骨细胞缺陷小鼠中废用诱导的骨丢失恢复的能力（目的2）。我们的研究结果将揭示IFF调节骨重建的细胞机制的基本见解，并将代表基于IFF的机械转导的骨丢失治疗的发展的一个相当大的进步。与公共卫生的相关性：骨质疏松症是2800万美国人的主要健康风险。这项研究将揭示骨内不同细胞如何协调其反应以驱动骨重建以响应间质液流动的基本见解。我们的研究结果将代表一个相当大的进步，对骨丢失的治疗方法的基础上的能力，骨细胞的感觉和响应的流体流动。

DESCRIPTION (provided by applicant): A large body of evidence suggests that skeletal interstitial fluid flow (IFF) mediates bone remodeling in response to mechanical loading. Our long-term goal is to develop treatments for bone loss based on bone cell mechanotransduction of IFF. A crucial step towards this goal is to understand how the responses of bone cells exposed to IFF result in bone remodeling. Recently, Tatsumi and colleagues generated a transgenic mouse model with inducible osteocyte ablation. Interestingly, although these mice were resistant to bone loss upon hindlimb suspension, mechanotransduction in these mice upon reloading was normal. This gives rise to the intriguing possibility that while osteocytes regulate IFF-mediated bone loss, increases in IFF during reloading may induce bone formation by direct stimulation of other types of bone cells. Our central hypothesis is that IFF mediates the bone resorption and formation that occur during unloading and reloading by two distinct mechanisms. During unloading, lack of IFF results in osteocyte- mediated bone resorption. During reloading, increased IFF induces bone formation by direct stimulation of osteoblasts or their progenitors. Recently, our lab has developed a novel microfluidic device for generating dynamic IFF in the femurs of hindlimb suspended mice. The device will be used to determine the role of osteocytes in mediating flow-induced bone remodeling within a native tissue environment. Specifically, we will first induce IFF in hindlimb suspended mice with and without ablated osteocytes to determine the capacity of IFF to inhibit osteoclastic activity upon disuse, and the role of osteocytes in mediating this process (aim 1). Next, by imposing a period of hindlimb suspension pre-osteocyte ablation, we will determine the capacity of IFF to stimulate recovery of disuse-induced bone loss in osteocyte-deficient mice (aim 2). Our findings will reveal fundamental insight into the cellular mechanisms involved in IFF-regulated bone remodeling and will represent a considerable advancement towards development of therapies for bone loss based on mechanotransduction of IFF. Relevance to Public Health: Osteoporosis is a major health risk for 28 million Americans. This study will reveal fundamental insight into how different cells within bone coordinate their responses to drive bone remodeling in response to interstitial fluid flow. Our findings will represent a considerable advancement towards development of therapies for bone loss based on the capacity of bone cells to sense and respond to fluid flow.