Signal Transduction Mechanism of Osteoclast Differentiation

骨形成和骨吸收的紧密平衡(称为骨重塑)维持着 骨骼的动态平衡。骨重建是成骨细胞和成骨细胞共同作用的结果。 骨吸收破骨细胞。这些功能相反的细胞通过旁分泌细胞信号进行通信 网络。平衡的转变有利于多核破骨细胞的形成，导致骨破坏，如 在自身免疫性关节炎、牙周病、绝经后骨质疏松症、帕吉特病等疾病中观察 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是 维持关键的骨骼动态平衡所必需的。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，BMP作用于破骨细胞 间接通过成骨细胞或基质细胞。骨形态发生蛋白2型(BMP-2)的精确机制 调节破骨细胞的活性是这一提案的关键问题。这将在治疗方面产生影响 为美国退伍军人常见的骨骼退行性疾病设计药物。 BMP与其细胞表面受体相互作用激活Smad信号通路。我们有 Smad信号在BMP-2诱导的成骨细胞集落刺激表达中的作用 因子-1(CSF-1)，破骨细胞生成的关键调节因子。我们的初步实验证明 Smad信号参与BMP-2诱导的关键成骨细胞转录因子的表达 Osterix(OSX)。此外，在这项提案中，我们首次表明BMP-2促进成骨细胞 另一种重要的破骨细胞形成蛋白--核因子受体激活剂B配体(RANKL)和 激活激活的T细胞核因子c1(NFATc1)，它是破骨细胞生成的主要调节因子。这个 该方案中要检验的假设是BMP-2激活转录因子osterix(OSX)和 NFATc1调控集落刺激因子-1和RANKL的表达，从而启动 破骨细胞的吸收活性。在第一个具体目标中，我们将研究两个关键转录因子的作用 OSX和NFATc1调节破骨细胞基因(RANKL和CSF-1)表达的因素 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OSX和NFATc1在成骨细胞中的表达和激活在第三个具体目标中，我们将 检测OSX和NFATc1在BMP-2诱导的破骨细胞生成中的功能参与。我们将进行关键测试 BMP-2参与激活这些重要的转录因子导致破骨细胞分化 采用免疫印迹、免疫组织化学、原位杂交、芯片分析和qRTPCR等技术。在……里面 在这项建议中，我们还将探索BMP-2-2对OSX基因表达的新的转录后调控。 诱导的microRNA。我们的结果将展示BMP-2如何协调复杂的转录 在成骨细胞中的网络，以严格调控破骨细胞的激活。

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.