A Novel Proteoglycan-4 Isoform Drives Skeletal Regeneration

Proteoglycan 4 (PRG4) is an extracellular matrix protein best known for its lubricating role in articular cartilage. Using a murine model of tibial fracture, we performed RNA-seq across multiple post-fracture timepoints and observed high Prg4 expression during the first week of healing, coinciding with the initial inflammatory phase. Single-cell RNA-seq of the fracture callus localized Prg4 expression to a stem cell population with key roles in repair. Analysis of alternative splicing in callus RNA identified a unique Prg4 isoform lacking three coding exons (hereafter termed Prg4-S). In vivo knockdown of Prg4-S using locally delivered siRNA produced multiple defects that culminated in impaired bone formation. Together, these findings uncover an unanticipated osteogenic role for a unique Prg4 splicing isoform and highlight its potential for translational applications.