Talking Back: leveraging dysfunctional osteoclasts to identify novel pathways of osteoclast-osteoblast communication

项目摘要 适当的骨结构依赖于骨吸收破骨细胞之间分子信号的复杂相互作用 (OCs)和骨形成成骨细胞（OB）。为了保持骨骼的完整性，骨形成必须与 再吸收--即OC必须与OB“对话”。这种偶联需要将骨祖细胞募集到 再吸收表面这一过程在石骨症（字面意思是“石骨”）中受到干扰， 尽管OC功能障碍，但仍持续存在，吸收水平非常低。再吸收与 形成不完全理解，但似乎需要OC。 我们描述了两个新的小鼠模型失调耦合。Nfatc 1条件性缺失的小鼠， 成熟OC中OC转录程序的驱动因子（Ctks-Cre; Nfatc 1fl/fl，此后称为Nfatc 1DOC）具有 增殖的RUNX 2+、碱性磷酸酶表达的成骨细胞前体在其骨髓中积累。 突变OC是必要的和足够的成骨细胞前体扩张。我们观察到类似的 在Slc 4a 2-/-小鼠（牛骨石化病模型）中的现象。我们的概念创新是， 在功能障碍的OC的情况下，偶联有助于骨质疏松。这一概念导致我们的总体 假设尽管存在不同的潜在遗传病变，但Nfatc 1DOC小鼠中功能障碍的OC具有以下特征： 常见的分子紊乱的耦合过程与小鼠和斑马鱼模型的骨石症。在 目的1，我们提出了转录组学分析，以确定共同的差异调节OC特异性转录本， 这些模型作为OC：OB通信的候选介质。在目标2中，我们检验了以下特定假设： 石骨症的血液学损害是由OC依赖性骨髓腔闭塞引起的， 成骨细胞前体，使用小鼠模型和来自石骨症个体的人类活检样本， 在体内验证我们的假设 这些研究利用了技术创新，包括分离原发性OC的纯人群， 先进的分子骨组织学技术来询问基因表达，并得到了 在OC生物学（查尔斯博士），斑马鱼遗传学和骨骼学方面具有专业知识的杰出合作者团队 开发（Henke博士），分子骨组织学（Andersen博士）和生物信息学专业知识（Center for 由沃曼博士运行的Skeleton Research骨测序核心）。这项工作将提供洞察正常OC：OB 骨重建过程中的偶联，有可能确定骨疾病的新治疗靶点， 偶联不是不适当地低（骨质疏松症）就是不适当地高（骨硬化症）。

PROJECT SUMMARY Proper bone structure relies on a complex interplay of molecular signals between bone resorbing osteoclasts (OCs) and bone forming osteoblasts (OBs). For skeletal integrity to be maintained, bone formation must match resorption—that is OC must “talk back” to OB. This coupling requires recruitment of osteoprogenitors onto the resorption surface. This process is perturbed in osteopetrosis (literally, “stone bone”), where bone formation continues despite dysfunctional OC with very low levels of resorption. The signals coupling resorption to formation are not fully understood, but appear to require OC. We describe two new mouse models of dysregulated coupling. Mice with conditional deletion of Nfatc1, the key driver of the OC transcriptional program, in mature OC (Ctks-Cre;Nfatc1fl/fl, henceforth Nfatc1DOC) have accumulation of proliferating RUNX2+, alkaline phosphatase-expressing osteoblastic precursors in their marrow. Mutant OC are both necessary and sufficient for this osteoblastic precursor expansion. We observe a similar phenomenon in Slc4a2-/- mice, a model of bovine osteopetrosis. Our conceptual innovation is that dysregulated coupling contributes to osteosclerosis in the settings of dysfunctional OC. This concept leads to our overarching hypothesis that, despite disparate underlying genetic lesions, dysfunctional OC in Nfatc1DOC mice share a common molecular derangement of the coupling process with mouse and zebrafish models of osteopetrosis. In Aim 1, we propose transcriptomic analysis to identify differentially regulated OC-specific transcripts common to these models as candidate mediators of OC:OB communication. In Aim 2, we test the specific hypothesis that hematologic impairment in osteopetrosis is caused by OC-dependent obliteration of the marrow space by osteoblastic precursors, using mouse models and human biopsy samples from individuals with osteopetrosis to validate our hypothesis in vivo. These studies leverage technical innovations including the isolation of pure populations of primary OC and advanced molecular bone histology techniques to interrogate gene expression and are supported by an outstanding team of collaborators with expertise in OC biology (Dr. Charles), zebrafish genetics and skeletal development (Dr. Henke), molecular bone histology (Dr. Andersen), and bioinformatic expertise (Center for Skeletal Research bone sequencing core run by Dr. Warman). This work will provide insight into normal OC:OB coupling during bone remodeling, with the potential to identify new therapeutic targets for bone diseases where coupling is either inappropriately low (osteoporosis) or inappropriately high (osteopetrosis).