CXCL12-ACKR3 Signaling Drives Fibrosis and Inflammation in Frozen Shoulder: A Single-Cell Guided Therapeutic Discovery

Frozen shoulder, a debilitating condition marked by chronic joint stiffness and pain, remains poorly understood due to unclear molecular drivers of its hallmark fibrosis and inflammation. Although fibroblast dysfunction contributes to FS pathology, specific pathogenic subsets remain unidentified. Through single-cell RNA sequencing of human synovial tissues, we discovered a distinct CXCL12-enriched fibroblast population (F1) driving disease progression via ACKR3 signaling. This axis exacerbated metalloproteinase (MMP)/tissue inhibitor of metalloproteinase (TIMP) dysregulation, promoting collagen overproduction and fibrotic niche formation. In vitro interventions demonstrated that both CXCL12 neutralization (Lit-927) and ACKR3 knockout effectively reduced pro-fibrotic responses by mitigating MMP/TIMP imbalance. Rat FS models recapitulated these findings, showing attenuated fibrosis following CXCL12 blockade. Our study establishes CXCL12-ACKR3 signaling as the central mechanism connecting fibroblast heterogeneity to extracellular matrix dysregulation in FS pathogenesis. These findings provide dual therapeutic strategies targeting ligand-receptor interactions for a condition currently managed only through symptomatic relief.