Exploring complex cellular interactions: mathematical modeling and experimental studies of bone turnover

理论基础：骨的力学性能取决于骨重建的过程，骨重建涉及破骨细胞的吸收，然后由以骨多细胞单位(BMU)组织的成骨细胞形成新骨。骨重建受局部和全身生化因素的调节。机械力也调节骨细胞的活动，并引导BMU的运动。骨细胞对机械力的反应包括骨细胞内变形诱导的变化，以及调节细胞间通讯的可溶性因子的产生的变化，如三磷酸腺苷。我的计划的目标是了解机械力如何调节骨骼细胞的即时活动及其执行生理功能的能力，以及单个细胞的物理环境如何整合到骨骼作为器官的表现中。 当前目标： 1.研究单个骨细胞如何整合机械力信息。 2.研究机械力在骨细胞内诱导的细胞间短程通讯。 3.将对单个细胞力学敏感性的描述纳入骨转换的组织尺度数学模型。 方法：我们建立了局部成骨细胞膜变形导致钙通道开放和胞浆钙升高，这在诱导细胞微损伤时表现出阈值特性。结合钙通道动力学和细胞内钙处理的数学模型将被用来研究阈值的形成。模型预测将使用原子力和单个成骨细胞的荧光显微镜进行测试。对单个细胞的机械刺激也被发现导致可溶性介质(被确认为ATP)的释放，从而在邻近的未连接的细胞中引起延迟的次级反应。由于这种反应随距离刺激细胞的距离而变化，我们假设细胞外的ATP降解为ADP会导致不同的核苷酸受体在离刺激细胞不同的距离处被激活。考虑到从原细胞释放的ATP的扩散和降解的数学模型将被用来预测离受刺激细胞不同距离处的ATP/ADP水平。我们将使用RNA干扰来研究单个核苷酸受体的作用。我们之前已经建立了一个偏微分方程模型，描述了生物化学引导的BMU在骨组织中的运动。为了解释力学因素对骨转换的影响，我们将成骨细胞和破骨细胞的力学敏感性模型合并到BMU模型中。 影响：这项工作将有助于更好地理解涉及不同细胞类型之间复杂的生化和机械相互作用的系统的空间和时间调节原理，这是发育生物学中的一个关键问题。

RATIONALE: Bone mechanical properties depend on the process of bone remodeling, which involves resorption by osteoclasts, followed by formation of new bone by osteoblasts organized in Bone Multicellular Units (BMUs). Bone remodeling is regulated by local and systemic biochemical factors. Mechanical forces also regulate the activity of the bone cells and guide BMU movement. The responses of bone cells to mechanical forces involve deformation-induced changes within bone cells, and alterations in the production of soluble factors, such as ATP, that regulate cell-cell communications. The goal of my program is to understand how mechanical forces regulate bone cells immediate activity and their ability to perform physiological function, and how physical environment of individual cells is integrated in the performance of bone as an organ. CURRENT OBJECTIVES: 1. To examine how mechanical force information is integrated by an individual bone cell. 2. To investigate short-range cell-cell communications induced by mechanical forces in bone cells. 3. To incorporate the description of the mechanosensitivity of individual cells into the tissue scale mathematical model of bone turnover. METHODOLOGY: We established that local osteoblast membrane deformation leads to calcium channels opening and elevation of cytosolic calcium, which exhibits threshold properties when cell micro-injury is induced. Mathematical model combining the calcium channel dynamics with intracellular calcium handling will be used to study the threshold formation. Model predictions will be tested using atomic force and fluorescence microscopy of individual osteoblasts. Mechanical stimulation of a single cell was also found to lead to the release of soluble mediator (identified as ATP), which induced delayed secondary responses in neighboring non-connected cells. Since the response changed with the distance from the stimulated cell, we hypothesize that extracellular degradation of ATP to ADP leads to activation of distinct nucleotide receptors at different distance from the stimulated cell. Mathematical model accounting for diffusion and degradation of ATP released from the primary cell will be used to predict ATP/ADP levels at different distance from the stimulated cell. We will examine the roles of individual nucleotide receptors using RNA interference. We have previously developed a partial differential equation model describing the biochemically guided BMU movement through the bone tissue. To account for steering of bone turnover by mechanical factors, we will incorporate the models of mechanosensitivity of osteoblasts and osteoclasts into the BMU model. IMPACT: This work will contribute to a better understanding of the principles of spatial and temporal regulation of systems involving complex biochemical and mechanical interactions among different cell types, a key question in developmental biology.