Is Mitf the Missing Puzzle Linking NFATc1 to Osteoclastogenesis

描述（由申请人提供）：破骨细胞是通过建模和重塑维持骨量所必需的骨吸收细胞。在病理性溶骨性条件下，破骨细胞被环境因素激活，这破坏了骨形成和骨吸收之间的平衡，并使平衡向骨丢失倾斜。尽管近年来口腔修复医学取得了很大进展，但治疗和控制口腔慢性骨丢失仍然是牙科医生面临的最具挑战性的任务之一。这种情况影响着世界各地数百万人，通常与永久性牙齿脱落有关。虽然药理学药物如双膦酸盐在预防与绝经相关的代谢性骨丢失方面取得了很大的成功，但它在预防牙周炎中的骨丢失方面无效[8]。在牙周炎中，口腔细菌感染释放的趋化因子从外周血循环中募集B和T细胞，这些免疫细胞是RANKL的重要局部来源，RANKL促进破骨细胞生成，导致慢性牙槽骨丢失。为了开发针对不受调节的破骨细胞活化的有效治疗方法，我们需要知道分化信号如何从破骨细胞表面受体传递到下游靶点，以及单个分子如何连接在一起形成网络。对自然突变和转基因的石骨症小鼠的研究揭示了许多重要的基因参与破骨细胞的发生。其中，Mitf的独特之处在于其组织特异性作用仅限于黑素细胞、肥大细胞和破骨细胞。虽然破骨细胞特异性Mitf从未被鉴定，但存在黑素细胞特异性Mitf和肥大细胞特异性Mitf，认为其负责谱系特异性基因激活。在破骨细胞生成的所有必需转录因子中，NFATc 1被认为是主转录因子，即使在不存在RANKL的情况下，其激活也会开启破骨细胞生成。尽管如此，目前尚不清楚一个普遍存在的因子，如NFATc1是如何能够指导破骨细胞特异性分化程序。我们建议，Mitf，通过其组织特异性的影响，是主要的候选人提供破骨细胞特异性转录调控NFATc1。在这个建议中，我们将研究是否存在于破骨细胞中的两个主要的Mitf亚型能够提供破骨细胞特异性的转录调控，以协助NFATc1在编排破骨细胞。我们将确定这两种亚型在促进破骨细胞生成和反式激活下游靶点的能力方面是否存在差异。我们还将确定它们与NFATc1的关系。实验提出检查Mitf是否以及如何与NFATc1通路相互作用。已知Mitf与NFATc1在Mitf和NFATc1共有的一些转录靶点上协同作用。我们还将检查两种Mitf亚型与NFATc 1在这些复合转录靶点上协同作用的能力。拟议的项目将使我们能够解开破骨细胞特异性作用的Mitf在破骨细胞生成，并确定哪种亚型是负责协助NFATc1掌握破骨细胞分化。 公共卫生相关性：NFATc1是破骨细胞生成的主要转录因子。然而，目前尚不清楚一个普遍存在的因子，如NFATc1是如何能够指导破骨细胞特异性分化程序。我们认为，Mitf，通过其组织特异性的影响，是主要的候选人，提供破骨细胞特异性转录调控连接NFATc1破骨细胞分化。

DESCRIPTION (provided by applicant): Osteoclasts are bone-resorbing cells essential for maintaining bone mass through modeling and remodeling. In pathological osteolytic conditions, osteoclasts are activated by environmental factors, which disrupt the balance between bone formation and bone resorption, and tip the equilibrium to bone loss. Despite recent advances in restorative dentistry, treating and controlling chronic bone loss in oral cavity is still one of the most challenging tasks for dentists. The condition affects millions of people around the world and is often associated with permanent tooth loss. Although pharmacological agents such as bisphosphonate have much success in preventing metabolic bone loss associated with menopause, it is not effective in preventing bone loss in periodontitis [8]. In periodontitis, chemotactic factors released from oral bacterial infection recruit B and T cells from peripheral blood circulation, and these immune cells are the important local sources of RANKL, which promotes osteoclastogenesis, leading to chronic alveolar bone loss. To develop effective treatment against unregulated osteoclast activation, we need to know how differentiation signals are transmitted from osteoclast surface receptors to the downstream targets and how individual molecules are linked together as a network. Studies of naturally mutated and transgenic osteopetrotic mice have revealed many important genes involving in osteoclastogenesis. Among these, Mitf is unique in its tissue-specific effects restricted to melanocytes, mast cells and osteoclasts. Although osteoclast-specific Mitf has never been identified, melanocyte-specific Mitf and mast cell-specific Mitf are present, believing to be responsible for lineage-specific gene activation. Among all the essential transcription factors in osteoclastogenesis, NFATc1 is considered the master transcription factor, which activation turns on osteoclastogenesis even in the absence of RANKL. Nonetheless, it is not clear how a ubiquitous factor like NFATc1 is able to direct an osteoclast-specific differentiation program. We propose that Mitf, through its tissue-specific effects, is the prime candidate to provide osteoclast-specific transcriptional regulation for NFATc1. In this proposal, we will examine whether the two major Mitf isoforms present in osteoclasts are able to provide osteoclast-specific transcriptional regulation to assist NFATc1 in orchestrating osteoclastogenesis. We will determine if there are differences between the two isoforms in their abilities to promote osteoclastogenesis and transactivate downstream targets. We will also determine their relationships with NFATc1. Experiments are proposed to examine whether and how Mitf interacts with the NFATc1 pathway. Mitf is known to synergize with NFATc1 on some transcriptional targets shared by Mitf and NFATc1. We will also examine the ability of the two Mitf isoforms in synergizing with NFATc1 on these compound transcriptional targets. The proposed project will allow us to unravel the osteoclast-specific role of Mitf in osteoclastogenesis and to determine which isoform is responsible in assisting NFATc1 to master osteoclast differentiation. PUBLIC HEALTH RELEVANCE: NFATc1 is the master transcription factor of osteoclastogenesis. However, it is not clear how a ubiquitous factor like NFATc1 is able to direct an osteoclast-specific differentiation program. We propose that Mitf, through its tissue-specific effects, is the prime candidate that provides osteoclast-specific transcriptional regulation to link NFATc1 to osteoclast differentiation.