Abstract
<jats:p>Paget's disease of bone (PDB) is a late-onset skeletal disorder characterized by excessive osteoclast-mediated bone remodelling and disorganized bone deposition. The P937R mutation in the ZNF687 gene causes a severe form of PDB complicated by giant cell tumour transformation. Although ZNF687 has been implicated in osteoclastogenesis, whether it regulates upstream haematopoietic progenitor dynamics and bone marrow myeloid output remains unclear. Using a constitutive Zfp687 knock-out mouse model, we showed that Zfp687 loss causes postnatal growth restriction, reduced bone marrow cellularity, impaired osteoclast differentiation in vitro and in vivo, and increased trabecular bone mass during adulthood. Flow cytometry revealed a marked reduction in osteoclast progenitors and macrophages in Zfp687-deficient bone marrow, whereas the pagetic P937R mutation promoted the expansion of the same myeloid populations in the Zfp687P937R knock-in mouse model. Single-cell RNA sequencing of bone marrow-derived c-Kit+ haematopoietic progenitors further demonstrated that Zfp687 loss selectively disrupted the myeloid progenitor compartment. This analysis identified 22 transcriptionally distinct populations and revealed a significant depletion of the early cycling granulocyte-monocyte progenitor cluster, without evidence of a global block in myeloid differentiation. Mechanistically, Zfp687 deficiency impaired the Brd4-c-Myc-NFATc1 axis in osteoclastogenic precursors and reduced Csf1 expression in bone marrow stromal and osteoblastic cells, linking intrinsic transcriptional competence to niche-derived M-CSF support. In pagetic patient iPSCs-derived haematopoietic progenitors, the P937R mutation enhanced clonogenic haematopoietic output, accelerated colony formation, and promoted the expansion of primitive/multipotent colony-forming progenitors, leading to hypercellular myeloid colonies. Together, our findings establish ZNF687 as a regulator of haematopoietic progenitor dynamics that couples bone marrow myeloid output to osteoclastogenesis, providing a progenitor-level mechanism for severe ZNF687-related PDB.</jats:p>