Deciphering the role of Piezo proteins in mechanotransduction of bone cells

骨基质通过两种不同细胞类型（骨形成成骨细胞和骨吸收破骨细胞）的平衡活动不断重塑。骨重塑也受到终末分化的成骨细胞（即骨细胞）的影响，骨细胞在矿化骨基质内形成细胞网络，并可能充当机械载荷的传感器。尽管已经提出了几种候选分子参与骨细胞的机械转导能力，但骨细胞网络的生理复杂性阻碍了主要控制骨骼机械生物学的明确途径的建立。机械敏感离子通道的一个潜在相关家族由两种蛋白质Piezo 1和Piezo 2组成。虽然这两种广泛表达的压电通道的生理相关性刚刚开始被解开，但它们对机械转导的影响已经在各种非骨骼细胞类型中得到证实。在我们与该项目相关的初步工作中，我们观察到i）成骨细胞特异性Piezo 1失活的小鼠显示出严重的骨质疏松表型ii）成骨细胞中的Piezo 1表达由体外和体内的机械应力诱导。这些数据有力地表明，Piezo 1在响应机械刺激的骨量调节中起着关键作用。我们的工作计划旨在特异性地灭活三种不同骨重建细胞类型中的Piezo 1和/或Piezo 2，并在细胞和分子水平上分析相应的小鼠模型。为了证明Piezo 1在骨细胞力学转导中的潜在作用，我们将应用尺骨负荷模型来监测成骨细胞或骨细胞中缺乏Piezo 1的小鼠的反应。最后，我们将进行一系列的细胞培养实验，从分子水平上了解压电蛋白在骨细胞力学传导中的功能。因此，我们期望获得新的和生理相关的见解机械生物学的骨骼。

The bone matrix is continuously remodeled through the balanced activities of two distinct cell types, bone-forming osteoblasts and bone-resorbing osteoclasts. Bone remodeling is also influenced by terminally differentiated osteoblasts, i.e. osteocytes, which form a cellular network within the mineralized bone matrix and presumably act as sensors of mechanical loading. Although several candidate molecules have been suggested to be involved in the mechanotransduction ability of osteocytes, the physiological complexity of the osteocyte network has hindered the establishment of a definite pathway primarily controlling the mechanobiology of the skeleton. One potentially relevant family of mechanosensitive ion channels is comprised of two proteins, Piezo1 and Piezo2. Although the physiological relevance of the two broadly expressed Piezo channels is just beginning to be unraveled, their impact on mechanotransduction has already been confirmed in various non-skeletal cell types. In our preliminary work related to this project we observed i) that mice with an osteoblast-specific Piezo1 inactivation display a severe osteoporotic phenotype ii) and that Piezo1 expression in osteoblasts is induced by mechanical stress, both in vitro and in vivo. These data strongly suggest that Piezo1 plays a key role in bone mass regulation in response to mechanical stimulation.Our working program aims at specifically inactivating Piezo1 and/or Piezo2 in the three different bone remodeling cell types and to analyze the respective mouse models at a cellular and molecular level. To demonstrate the potential role of Piezo1 in bone cell mechanotransduction we will apply the ulna loading model to monitor the response of mice lacking Piezo1 in osteoblasts or osteocytes. Finally, we will pursue a series of cell culture experiments to understand the function of Piezo proteins in bone cell mechanotransduction at a molecular level. We thereby expect to obtain novel and physiologically relevant insights into the mechanobiology of the skeleton.