Hyperactive BMP and Mechanosignaling Remodel Chromatin to Drive Aberrant Osteogenesis in Fibrodysplasia Ossificans Progressiva (ATAC-Seq)

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder in which a recurrent ACVR1 (R206H) mutation drives progressive heterotopic ossification (HO). We combined super-resolution stochastic optical reconstruction microscopy (STORM), transposase-accessible chromatin with sequencing (ATAC-Seq), and RNA sequencing (RNA-Seq) to investigate how Acvr1R206H remodels chromatin to promote osteogenic transcriptional programs. Mutant mouse embryonic fibroblasts (MEFs) exhibited globally decondensed chromatin and increased accessibility at developmental and osteogenic loci enriched for HOX, TEAD, and RUNX motifs. Integration of ATAC-Seq and RNA-Seq data identified transcriptional networks primed for osteochondrogenic gene expression, including ossification, extracellular matrix organization, and cell adhesion pathways, consistent with enhanced BMP-SMAD and mechanotransduction activity. Pharmacological modulation showed that chromatin alterations were dynamic and reversible: activation of Rho/ROCK in wild-type cells reproduced the mutant chromatin state, while inhibition of Rho/ROCK or BMP-SMAD signaling restored condensation to wild-type levels in mutant cells. These findings establish that Acvr1R206H enforces a pro-osteogenic chromatin landscape through convergent BMP-SMAD and Rho/ROCK signaling.