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

项目总结 适当的骨结构依赖于骨吸收破骨细胞之间复杂的分子信号相互作用 (OCS)和成骨细胞(OBS)。为了保持骨骼的完整性，骨的形成必须匹配 再利用--也就是OC必须向OB“回话”。这种结合需要将骨祖细胞招募到 再吸收表面。这一过程在骨化症(字面意思是“石骨”)中被干扰，在那里骨形成 尽管OC功能障碍，但吸收水平非常低，但仍在继续。将再吸收耦合到 形成没有被完全理解，但似乎需要OC。 我们描述了两个新的失调耦合的小鼠模型。小鼠有条件地删除了关键基因NFATc1 OC转录程序的驱动程序，在成熟的OC(Ctks-Cre；Nfulc1fl/fl，以下简称Nfulc1DOC)中具有 增殖中的RUNX2+，表达碱性磷酸酶的成骨前体细胞在骨髓中的积聚。 突变的OC对于成骨前体细胞的扩张既是必要的也是充分的。我们观察到一个类似的 牛骨化症模型Slc4a2-/-小鼠的实验现象。我们的理念创新是，监管不规范 在OC功能障碍的情况下，偶联作用会导致骨硬化。这一概念导致了我们的总体 假设，尽管存在不同的潜在遗传损伤，但Nafc1DOC小鼠功能障碍的OC共享一个 小鼠和斑马鱼骨化症模型偶联过程中常见的分子紊乱。在……里面 目的1，我们建议进行转录转录分析以确定共同的差异调控的OC特异性转录本 这些模型作为OC：OB沟通的候选中介。在目标2中，我们测试了特定的假设 骨质疏松症的血液学损害是由OC依赖的骨髓间隙闭塞引起的 成骨前体细胞，使用小鼠模型和来自骨化症患者的人类活检样本 在体内验证我们的假设。 这些研究利用了技术创新，包括隔离初级OC和 先进的分子骨组织学技术用于询问基因表达，并得到 在OC生物学(Charles博士)、斑马鱼遗传学和骨骼方面具有专业知识的杰出合作者团队 发展(亨克博士)、分子骨组织学(安德森博士)和生物信息学专业知识( 由沃曼博士运营的骨骼研究骨骼测序核心)。这项工作将提供对正常OC：OB的深入了解 骨重建过程中的偶联，有可能确定骨疾病的新治疗靶点 联结度过低(骨质疏松)或过高(骨质疏松症)。

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).