Regulation of Osteoclastogenesis by Calcium

描述（由申请人提供）：我们将研究钙对破骨细胞发生的调控，重点研究最近发现的钙释放激活钙通道途径。破骨细胞吸收的激活是病理性骨破坏的最终共同途径，Ca2+信号对于rankl刺激的破骨细胞发生至关重要。在破骨细胞前体中，Ca2+信号激活转录调节因子NFATc1，其驱动破骨细胞特异性蛋白的表达。NFATc1的其他作用包括在破骨细胞前体融合中的作用，目前尚未明确。然而，Ca2+通量调节分化的时空模式在很大程度上是未知的。我们在体外鉴定了钙释放激活钙通道Orai1作为破骨细胞前体细胞外Ca2+内流的介质。在体外人破骨细胞分化中，我们发现Orai1缺失或抑制可阻断成熟多核破骨细胞的形成，并大大降低骨矿物质的吸收。对Orai1-/-小鼠的体内研究显示了类似的变化，并与骨骼异常相关，证实了Orai1在骨骼调节中的重要性。我们假设Orai1介导关键的Ca2+信号，通过控制前体细胞融合来调节破骨细胞的形成。在目的1中，我们将在体内定义Orai1在破骨细胞前体中的功能。我们将生成一只允许组织选择性地从破骨细胞前体中删除Orai1的小鼠。这将避免Orai1完全缺乏的陷阱，这种缺陷会影响多种细胞类型，导致早期死亡。我们将比较一种新的组织选择性Orai1敲除小鼠的骨骼效应与全球Orai1敲除小鼠的骨骼效应，以区分Orai1对破骨细胞发生和骨骼调节的直接和间接影响。我们将分析体内破骨细胞前体中选择性Orai1缺乏对骨骼的影响，并确定由破骨细胞前体中Orai1缺失引起的分化异常。在Aim 2中，我们将确定Orai1钙信号通过调节破骨细胞前体基因转录来调节破骨细胞形成，特别是细胞融合的机制。这项工作将包括通过测量野生型和Orai1缺陷细胞中与破骨细胞分化和活性相关的Ca2+振荡来确定Orai1依赖性Ca2+通量对破骨细胞分化信号的响应。通路分析将进一步确定nfatc1调节的基因表达是Orai1缺陷和WT细胞中Ca2+激活的功能，我们将识别和分析依赖于Orai1的融合相关基因。这些研究将明确Orai1调控破骨细胞发生的机制，这将指导开发新的策略来控制病理性破骨细胞活动。

DESCRIPTION (provided by applicant): We will study regulation of osteoclastogenesis by calcium, focusing on a recently discovered calcium-release activated calcium channel pathway. Activation of osteoclast resorption is the final common pathway in pathologic bone destruction, and Ca2+ signaling is critical to RANKL-stimulated osteoclastogenesis. In osteoclast precursors, Ca2+ signals activate the transcriptional regulator NFATc1, which drives expression of osteoclast-specific proteins. Other effects of NFATc1 include a role, now poorly defined, in fusion of osteoclast precursors. However, the the spatial and temporal patterns of Ca2+ fluxes regulating differentiation were largely unknown. We identified the calcium release activated calcium channel Orai1 as a mediator of extracellular Ca2+ influx in osteoclast precursors in vitro. In human osteoclast differentiation in vitro, we showed that absence or inhibition of Orai1 blocked the formation of mature multinucleated osteoclasts and greatly reduced bone mineral resorption. Studies of Orai1-/- mice showed similar changes in vivo, with associated with skeletal abnormalities, confirming the importance of Orai1 in bone regulation. We hypothesize that Orai1 mediates critical Ca2+ signals that regulate osteoclast formation by controlling the fusion of precursor cells. In Aim 1 we will define in vivo the function of Orai1 in osteoclast precursors. We will generate a mouse allowing tissue-selective deletion of Orai1 from osteoclast precursors. This will avoid pitfalls of complete Orai1 deficiency, which affects multiple cell type, leading to early mortality. We will compare the skeletal effects of a novel tissue-selective Orai1 knockout mouse to those of the global Orai1 knockout, to distinguish direct from indirect effects of Orai1 on osteoclastogenesis and skeletal regulation. We will analyze the skeletal effects of selective Orai1 deficiency in osteoclast precursors in vivo and identify abnormalities of differentiation caused by loss of Orai1 from osteoclast precursors. In Aim 2 we will determine the mechanisms by which Orai1 calcium signals modulate osteoclast precursor gene transcription to regulate osteoclast formation, particularly cell fusion. This work will include studies defining Orai1-dependent Ca2+ fluxes in response to osteoclast differentiation signals via measurement of Ca2+ oscillations with respect to osteoclast differentiation and activity in wild type and Orai1 deficient cells. Pathway analysis will, further, define NFATc1-regulated gene expression as a function of Ca2+ activation in Orai1-deficient and WT cells, and we will identify and analyze fusion- related genes dependent on Orai1. These studies will define mechanisms through which Orai1 regulates osteoclastogenesis, which will guide the development of new strategies to control pathologic osteoclastic activity.