CSPG4+ extracellular vesicles carry fibronectin and interleukin-11 and reflect radiographic severity in knee osteoarthritis.

To evaluate chondroitin sulfate proteoglycan 4 (CSPG4)+ plasma extracellular vesicles (EVs) as a novel biomarker for knee osteoarthritis (OA) severity across independent study cohorts. Radiographic and symptomatic OA severity were evaluated in participants from two separate institutions. EVs were isolated from plasma (discovery cohort, n = 51; validation cohort, n = 92) and synovial fluid (SF) (n = 61) from 204 OA patients and characterized by morphology, surface markers, and pathogenic cargo, and evaluated for associations with knee OA severity. Single-cell RNA sequencing datasets (GSE152805 and GSE216651) were used to elucidate the joint tissue localization of the genes of interest. Across both discovery and validation cohorts, plasma CSPG4+ EV frequencies showed positive correlations with knee radiographic OA severity scores, reflecting joint structural damage, but not with symptomatic OA severity. In OA joint tissues, particularly in damaged cartilage-derived chondrocytes, the CSPG4 gene was co-expressed with FN1 and IL11 genes, which encode the OA pathogenic mediators fibronectin (FN1) and interleukin-11 (IL-11). Consistent with this, OA SF CSPG4+ EVs carried higher proportions of FN1 and IL-11 compared with CSPG4- EVs, identifying these proteins as enriched pathogenic cargo of the CSPG4+ EV subset in OA. We identified CSPG4+ EV subpopulations in plasma as novel biomarkers of knee radiographic OA severity, reflecting underlying structural joint damage. In SF, CSPG4+ EVs were enriched in FN1 and IL-11, potent mediators of matrix remodeling and inflammatory signaling in OA, consistent with a role for CSPG4+ EV cargo in joint deterioration.