Deciphering the role of Piezo proteins in mechanotransduction of bone cells

骨基质是通过两种不同的细胞类型，成骨细胞和骨吸收破骨细胞的平衡活动不断重塑的。骨重塑也受到终分化成骨细胞（即骨细胞）的影响，骨细胞在矿化骨基质内形成细胞网络，并可能作为机械载荷的传感器。尽管一些候选分子被认为与骨细胞的机械转导能力有关，但骨细胞网络的生理复杂性阻碍了确定主要控制骨骼机械生物学的明确途径的建立。一个潜在相关的机械敏感离子通道家族由两种蛋白质组成，Piezo1和Piezo2。尽管这两种广泛表达的压电通道的生理相关性刚刚开始被揭示，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)具有成骨细胞特异性Piezo1失活的小鼠显示出严重的骨质疏松表型ii)以及体外和体内机械应力诱导成骨细胞中的Piezo1表达。这些数据有力地表明，Piezo1在响应机械刺激的骨量调节中起关键作用。我们的工作计划旨在在三种不同的骨重塑细胞类型中特异性灭活Piezo1和/或Piezo2，并在细胞和分子水平上分析各自的小鼠模型。为了证明Piezo1在骨细胞机械转导中的潜在作用，我们将应用尺骨负荷模型来监测缺乏Piezo1的小鼠在成骨细胞或骨细胞中的反应。最后，我们将进行一系列细胞培养实验，从分子水平上了解压电蛋白在骨细胞机械转导中的功能。因此，我们期望对骨骼的机械生物学获得新颖的和生理学上相关的见解。

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.