Mechanisms of osteocyte mechano-signaling and sclerostin regulation

项目总结 骨质疏松症和其他骨骼脆性疾病影响着全球2亿多人， 每年贡献约900万次制作。预防骨丢失和/或恢复患者丢失的骨量 对于限制骨骼脆性疾病对个人和经济的影响至关重要。中国的一个关键目标 刺激新骨形成的是硬化素蛋白，它是Wnt/β-catenin信号的拮抗剂 级联，这是由骨嵌入的骨细胞产生的。大量的骨合成代谢线索，包括 机械负荷，减少硬化素的表达，导致成骨细胞生成的“去抑制”和 刺激新骨形成。然而，骨细胞感觉机械性的关键机制细节 加载，将这些加载信号传递到生物效应器，这些生物效应器的身份以及如何 硬化素的生物利用度是否受到监管尚不清楚。我们的初步数据发现了一些新奇的 骨细胞如何感知和对机械提示做出反应的中介。具体来说，我们展示了微管- 依赖细胞骨架的硬度调节机械激活的钙离子内流。此外，我们还牵涉到TRPV4 作为一种主要的机械依赖性钙离子内流途径，驱动钙离子依赖性激活 钙/钙调蛋白依赖的激酶II(CaMKII)降低硬化素在骨细胞中的生物利用度。在 目前，我们将使用体外、体外和体内模型来确定MT密度和 细胞骨架交联化对骨细胞机械传感的影响 TRPV4通道开放对机械应力的响应，并阐明FFSS- 依赖于CaMKII的激活调节硬化素的降解和Sost基因的转录。这项工作将会有更多 全面解释硬化素的生物调节，将机械连接几个空白的知识 骨细胞如何感知和响应机械载荷，并将揭示改进或保存的新靶点 衰老和疾病中的骨量。

PROJECT SUMMARY Osteoporosis and other diseases of skeletal fragility affect more than 200 million people worldwide and contributes to ~9 million factures annually. Preventing bone loss and/or restoring lost bone mass in patients is of vital importance to limiting the personal and economic impact of diseases of skeletal fragility. A key target in the stimulation of new bone formation is the protein sclerostin, an antagonist of the Wnt/beta-catenin signaling cascade, which is produced by bone embedded osteocytes. Numerous osteoanabolic cues, including mechanical load, reduce expression of the sclerostin leading to “de-repression” of osteoblastogenesis and stimulation of de novo bone formation. However, key mechanistic details of how osteocytes sense mechanical load, transduce these load signals to biologic effectors, the identity of these biological effectors and how sclerostin bioavailability is regulated are unclear. Our preliminary data have uncovered a number of novel mediators of how osteocytes sense and respond to mechanical cues. Specifically, we show that microtubule- dependent cytoskeletal stiffness regulates mechano-activated Ca2+ influx. Furthermore, we implicate TRPV4 as a major mechano-dependent Ca2+ influx pathway that drives Ca2+ dependent activation of calcium/calmodulin-dependent kinase II (CamKII) to reduce sclerostin bioavailability in the osteocyte. In the present grant, we will use in vitro, ex vivo and in vivo models to determine the contribution of MT density and cytoskeletal crosslinking to osteocyte mechanosensing, define the contribution and mechanisms of osteocyte TRPV4 channel opening in response to mechanical stress and elucidate the mechanisms by which FFSS- dependent CamKII activation regulates sclerostin degradation and Sost gene transcription. This work will more fully explain the biological regulation of sclerostin, will mechanistically link several gaps in the knowledge of how osteocytes sense and respond to mechanical load, and will reveal novel targets to improve or preserve bone mass in aging and disease.