Integrative analysis reveals synergistic regulation of Sp7 by BRD9 and Wnt/β-catenin signaling during osteogenic differentiation.

Osteoporosis is a complex skeletal disorder characterized by low bone mineral density (BMD). Compared with classical epigenetic modifications, such as DNA methylation and histone modifications, the participation of chromatin-remodeling complexes in osteoporosis remains less explored. To identify chromatin remodeling factors causally associated with bone mineral density (BMD), here we conducted a systematic analysis of 87 genes encoding components of four major chromatin-remodeling complexes using Summary-data-based Mendelian randomization (SMR) analysis. Candidate chromatin-remodeling factors were further cross-referenced with publicly available skeletal phenotyping data from the International Mouse Phenotyping Consortium (IMPC) database. Functional validation revealed that non-canonical BAF (ncBAF) subunit BRD9 is essential for osteoblast differentiation using both in vitro cell culture and in vivo zebrafish models. RNA-Sequencing (RNA-Seq) demonstrated that BRD9 orchestrates osteogenic differentiation by modulating Wnt/β-catenin signaling activity. Mechanistically, the osteogenic master transcription factor Sp7 was identified as a direct transcriptional target of BRD9, whose expression is coordinately controlled through the synergistic interplay between BRD9 and Wnt/β-catenin signaling during osteogenesis. Collectively, this study established a comprehensive framework for identifying causal genes implicated in osteoporosis and elucidated the previously unrecognized regulatory role of BRD9 in osteogenesis.