Is Mitf the Missing Puzzle Linking NFATc1 to Osteoclastogenesis

描述(申请人提供)：破骨细胞是骨吸收细胞，通过建模和重塑维持骨量是必不可少的。在病理性溶骨条件下，破骨细胞被环境因素激活，破坏骨形成和骨吸收之间的平衡，使平衡倾向于骨丢失。尽管修复学近年来取得了进展，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以百万计的人，并经常与永久性牙齿脱落有关。虽然双膦酸类药物在预防更年期相关的代谢性骨丢失方面有很大的成功，但在预防牙周炎中的骨丢失方面效果不佳[8]。在牙周炎中，口腔细菌感染释放的趋化因子从外周血液循环中募集B和T细胞，这些免疫细胞是RANKL的重要局部来源，RANKL促进破骨细胞的形成，导致慢性牙槽骨丢失。为了开发有效的治疗方法来对抗不受调控的破骨细胞激活，我们需要知道分化信号是如何从破骨细胞表面受体传递到下游靶点的，以及单个分子是如何作为网络连接在一起的。对自然突变和转基因骨质疏松小鼠的研究发现了许多与破骨细胞形成有关的重要基因。其中，MITF的独特之处在于其组织特异性效应仅限于黑素细胞、肥大细胞和破骨细胞。尽管破骨细胞特异性的MITF从未被鉴定过，但黑素细胞特异性的MITF和肥大细胞特异性的MITF存在，它们被认为是导致谱系特异性基因激活的原因。在破骨细胞生成的所有必需转录因子中，NFATc1被认为是主要的转录因子，即使在RANKL缺失的情况下，它的激活也能启动破骨细胞的生成。然而，目前还不清楚像NFATc1这样的普遍存在的因子如何能够指导破骨细胞特异性分化程序。我们认为，MITF通过其组织特异性效应，是为NFATc1提供破骨细胞特异性转录调控的首选候选基因。在这项提案中，我们将研究破骨细胞中存在的两种主要MITF亚型是否能够提供破骨细胞特异性的转录调控，以帮助NFATc1协调破骨细胞的形成。我们将确定这两种异构体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。我们还将确定他们与NFATc1的关系。建议进行实验以检查MITF是否以及如何与NFATc1途径相互作用。已知MITF与NFATc1在MITF和NFATc1共有的一些转录靶点上具有协同作用。我们还将检测两种MITF亚型与NFATc1在这些复合转录靶点上协同作用的能力。这个拟议的项目将使我们能够解开MITF在破骨细胞形成中的破骨细胞特异性作用，并确定哪个亚型负责帮助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，目前还不清楚像NFATc1这样的普遍存在的因子如何能够指导破骨细胞特异性分化程序。我们认为，MITF通过其组织特异性效应，是提供破骨细胞特异性转录调控的首选候选基因，将NFATc1与破骨细胞分化联系起来。

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.