The ZNF687 mutation of Paget's disease associated with giant cell tumour causes severe bone remodelling alteration as a result of a deregulated osteoclast transcriptional program

Abstract

Pagets disease (PDB) is a late-onset bone remodelling disorder with a broad spectrum of symptoms and complications. One of the most aggressive forms is caused by the P937R mutation in the ZNF687 gene. Although the genetic involvement of ZNF687 in PDB has been extensively studied, the molecular mechanisms underlying this association remains unclear. Here, we describe the first Zfp687 knock-in mouse model and demonstrate that the mutation recapitulates the PDB phenotype, showing a severe bone remodelling alteration. Through micro-computed tomography analysis, we observed that 8-month-old mice showed a mainly osteolytic phase, with a significant decrease in the trabecular bone volume affecting the femurs and the vertebrae of both heterozygous and homozygous mutant mice. In contrast, osteoblast activity was deregulated, beginning to produce disorganised bone. Noteworthy, this phenotype became pervasive in 16-month-old mice, where osteoblast function overtook bone resorption as the predominant event, as highlighted by the presence of woven bone in histological analyses, consistent with the PDB phenotype. Furthermore, we detected osteophytes and intervertebral disc degeneration, outlining for the first time the link between osteoarthritis and PDB in a PDB mouse model. Finally, we generated CRISPR-Cas9-based Zfp687 knock-out RAW 264.7 cells, and noted a remarkable impairment of osteoclast differentiation capacity, reinforcing the relevance of Zfp687 during this process. RNA-sequencing on wild type and KO clones identified a set of genes involved in osteoclastogenesis under the control of Zfp687, i.e., Tspan7, Cpe, Vegfc, and Ggt1. Thus, this study established an essential role of Zfp687 in the regulation of bone remodelling, and may offer the potential to therapeutically treat PDB.