Excess FGFR3 signaling in achondroplasia disrupts turnover of resting zone chondrocytes via CREB signaling

Achondroplasia, associated with gain-of-function mutations in FGFR3, causes growth plate cartilage dysfunction, resulting in short-limb dwarfism. However, its precise molecular and cellular mechanisms remain unclear. To address this, we aimed to generate knock-in mice (Fgfr3Ach) harboring the achondroplasia mutation (p.Gly380Arg). In addition to previously reported abnormalities, we observed an expansion of the resting zone. EdU labeling and lineage tracing analysis revealed disrupted stem cell properties of resting zone chondrocytes, preventing self-renewal, limiting cell divisions and migration toward the primary ossification center. Single-cell RNA-seq and immunohistochemical analysis identified a cell cluster that corresponded to the expanded resting zone. Pathway analysis and functional experiments revealed that CREB disrupts stem cell properties in resting zone chondrocytes and contributes to dwarfism. Administration of CREB inhibitor 666-15 restored growth plate pathology and bone length. These findings demonstrate that how excess FGFR3 signaling disrupts resting zone chondrocyte properties and suggest potential therapeutic targets for achondroplasia. Overall design: We harvested growth plate cartilage from wild-type mice and knock-in mice bearing the p.Gly374Arg mutation in Fgfr3 (Fgfr3Ach) at 19- and 22-days old. We subjected these samples to scRNA-seq analysis.