Das Amitabh, Saeki Keita, Dell'Orso Stefania, Wang Xiaobei, Mansky Kim C, Stains Joseph, Ozato Keiko, Deng Hong-Wen, Thumbigere-Math Vivek
Division of Periodontology, University of Maryland School of Dentistry, MD, United States.
Molecular Genetics of Immunity Section, Division of Developmental Biology, National Institute of Child Health and Human Development (NICHD), MD, United States.
J Bone Miner Res. 2025 Jun 19. doi: 10.1093/jbmr/zjaf084.
Osteoclasts (OCs) are multinucleated bone resorbing cells essential for skeletal development and remodeling. In adulthood, OCs originate from the serial fusion of monocytes, yet the transcriptional and epigenetic mechanisms shaping their osteoclastogenic potential at a single cell resolution remain poorly understood. Here, we present an integrative multi-omics analysis, combining single-cell (sc) RNA-seq, scATAC-seq, bulk RNA-seq, and ChIP-seq, to comprehensively define the regulatory landscape of osteoclastogenesis in wild-type (WT) and Irf8 conditional knockout (cKO) mice. We uncovered a highly structured and sequential differentiation trajectory from hematopoietic stem and progenitor cells (HSPCs) to common monocyte progenitors (cMoPs) to mature monocytes, with each stage exhibiting distinct transcriptional and epigenetic signatures. cMoPs and monocytes are the critical stages when OC lineage priming occurs, characterized by transcriptional and epigenetic activation of cytoskeletal, immune, and cell migration pathways. This priming is tightly regulated to prevent premature OC differentiation, and IRF8 acts as a negative regulator of osteoclastogenesis by maintaining monocyte identity and restricting chromatin accessibility at osteoclastogenic loci. IRF8 deficiency disrupts this balance, leading to chromatin reprogramming characterized by increased accessibility at OC-promoting loci (Nfatc1, Cebpe) and reduced accessibility at monocyte-specific genes (Mafb, Klf4), thereby priming precursors toward pre-mature osteoclastogenesis. Just as NFATc1 is recognized as a master activator of osteoclastogenesis, our findings position IRF8 as a master negative regulator of osteoclastogenesis, maintaining the delicate balance required for proper bone homeostasis. Collectively, this study provides unprecedented resolution into the molecular mechanisms shaping OC precursor identity and offers novel insights into potential therapeutic targets for osteolytic disorders.
破骨细胞（OCs）是多核骨吸收细胞，对骨骼发育和重塑至关重要。在成年期，破骨细胞起源于单核细胞的连续融合，但在单细胞分辨率下塑造其破骨细胞生成潜能的转录和表观遗传机制仍知之甚少。在这里，我们进行了一项综合多组学分析，结合单细胞（sc）RNA测序、scATAC测序、批量RNA测序和ChIP测序，以全面定义野生型（WT）和Irf8条件性敲除（cKO）小鼠中破骨细胞生成的调控格局。我们发现了一条从造血干细胞和祖细胞（HSPCs）到普通单核祖细胞（cMoPs）再到成熟单核细胞的高度结构化且有序的分化轨迹，每个阶段都表现出独特的转录和表观遗传特征。cMoPs和单核细胞是破骨细胞谱系启动发生时的关键阶段，其特征是细胞骨架、免疫和细胞迁移途径的转录和表观遗传激活。这种启动受到严格调控以防止破骨细胞过早分化，而IRF8通过维持单核细胞身份并限制破骨细胞生成位点的染色质可及性，作为破骨细胞生成的负调节因子。IRF8缺乏会破坏这种平衡，导致染色质重编程，其特征是破骨细胞促进位点（Nfatc1、Cebpe）的可及性增加，而单核细胞特异性基因（Mafb、Klf4）的可及性降低，从而使前体细胞倾向于过早的破骨细胞生成。正如NFATc1被认为是破骨细胞生成的主要激活因子一样，我们的研究结果将IRF8定位为破骨细胞生成的主要负调节因子，维持适当骨稳态所需的微妙平衡。总的来说，这项研究为塑造破骨细胞前体身份的分子机制提供了前所未有的解析，并为溶骨性疾病的潜在治疗靶点提供了新的见解。
