Signal Transduction Mechanism of Osteoclast Differentiation

骨形成和骨吸收（称为骨重建）的紧密平衡维持了骨的生长。 骨骼的内环境稳定。骨重建通过成骨细胞和成骨细胞的协同作用发生， 骨吸收破骨细胞。这些功能上对立的细胞通过旁分泌细胞信号传导进行交流 网络有利于多核破骨细胞形成的平衡的转变导致骨破坏， 在诸如自身免疫性关节炎、牙周病、绝经后骨质疏松症、Padget's 疾病和骨肿瘤转移。另一方面，成骨细胞和破骨细胞的有序供应， 维持关键的骨平衡所需的能量骨形态发生蛋白（BMP）被用作 促进骨再生的治疗措施。最近的报道表明骨形成蛋白作用于破骨细胞 间接通过成骨细胞或基质细胞。BMP 2型（BMP-2） 调节破骨细胞的活性是该方案的关键问题。这将具有治疗意义， 针对美国退伍军人常见的骨退化疾病设计药物。 BMP与其细胞表面受体的相互作用激活Smad信号通路。我们有 证实了Smad信号在BMP-2诱导的成骨细胞表达殖民地刺激中的作用， 因子-1（CSF-1），破骨细胞生成的关键调节因子。我们的初步实验表明， Smad信号传导参与BMP-2诱导的关键成骨细胞转录因子的表达， 奥斯特里克斯（Osx）。此外，在这项研究中，我们首次发现BMP-2可以增加成骨细胞的增殖， 另一种关键的破骨细胞生成蛋白，NF B配体受体激活因子（RANKL）的表达， 激活活化T细胞核因子c1（NFATc 1），这是破骨细胞生成的主要调节因子。的 在该提议中待检验的假设是BMP-2激活转录因子osterix（Osx）， NFATc 1控制集落刺激因子-1（CSF-1）和RANKL的表达，以启动细胞凋亡。 破骨细胞的再吸收活性。在第一个具体目标中，我们将研究两个关键转录的作用， Osx和NFATc 1在调节破骨细胞生成基因（RANKL和CSF-1）表达中的作用 成骨细胞对BMP-2的反应。在第二个具体目标中，我们将研究其背后的机制 BMP-2诱导成骨细胞中Osx和NFATc 1的表达和活化。在第三个具体目标中，我们将 测试Osx和NFATc 1在BMP-2诱导的破骨细胞生成中的功能参与。我们将测试 BMP-2参与激活这些重要的转录因子，导致破骨细胞分化 使用免疫印迹、免疫组织化学、原位杂交、ChIP分析和qRTPCR技术。在 本研究还将探索BMP-2对Osx基因表达的新的转录后调控， 诱导的microRNA。我们的研究结果将证明BMP-2如何能够协调一个复杂的转录 成骨细胞中的神经网络紧密调节破骨细胞的活化。

A tight balance of bone formation and bone resorption (termed as the bone remodeling) maintains the homeostasis of the skeleton. The bone remodeling occurs by concerted action of bone forming osteoblasts and bone resorbing osteoclasts. These functionally opposing cells communicate via a paracrine cell signaling network. A shift in the balance in favor of multi-nucleated osteoclast formation causes bone destruction as observed in diseases such as autoimmune arthritis, periodontosis, postmenopausal osteoporosis, Padget's disease and bone tumor metastasis. On the other hand, an orderly supply of osteoblasts and osteoclasts are needed for maintaining the critical bone homeostasis. The bone morphogenetic proteins (BMPs) are used as therapeutic measures for promoting bone regeneration. Recent reports suggest that BMPs act on osteoclasts indirectly through osteoblasts or stromal cells. The precise mechanism by which BMP type 2 (BMP-2) regulates the osteoclast activity is the key question in this proposal. This will have therapeutic implications in designing drugs for the bone degenerating diseases common to the war veterans in the USA. Interaction of BMP with its cell surface receptors activates Smad signaling pathway. We have demonstrated a role for Smad signaling in BMP-2-induced osteoblastic expression of the colony stimulating factor-1 (CSF-1), a key regulator of osteoclastogenesis. Our preliminary experiments demonstrate an involvement of Smad signaling in BMP-2-induced expression of the critical osteoblastic transcription factor, osterix (Osx). Furthermore, in this proposal, we show for the first time that BMP-2 increases osteoblastic expression of another critical osteoclastogenic protein, the receptor activator of NF¿B ligand (RANKL) and activates nuclear factor of activated T cells c1 (NFATc1), a master regulator of osteoclastogenesis. The hypothesis to be tested in this proposal is that BMP-2 activates the transcription factors osterix (Osx) and NFATc1 to control the expression of colony stimulating factor-1 (CSF-1) and RANKL in order to initiate the resorptive activity by osteoclasts. In the first specific aim, we will investigate the role of two key transcription factors, Osx and NFATc1 in regulating expression of the osteoclastogenic genes (RANKL and CSF-1) in osteoblasts in response to BMP-2. In the second specific aim, we will examine the mechanism underlying BMP-2-induced expression and activation of Osx and NFATc1 in osteoblasts. In the third specific aim, we will test the functional involvement of Osx and NFATc1 in BMP-2-induced osteoclastogenesis. We will test critical involvement of BMP-2 in activating these important transcription factors leading to osteoclast differentiation using immunoblotting, immunohistochemistry, in situ hybridization, ChIP analysis and qRTPCR techniques. In this proposal we will also explore the novel post-transcriptional regulation of Osx gene expression by BMP-2- induced microRNAs. Our results will demonstrate how BMP-2 can orchestrate a complex transcriptional network in osteoblasts to tightly regulate osteoclast activation.