Fig. 1: Senescence of FLSs is associated with OA progression.

a Representative images of immunohistochemistry staining of p16^INK4a in normal and OA patients. n = 10 independent biological samples. Scale bar: 100 µm. b Representative images of immunofluorescence staining of p16^INK4a in synovium from normal and OA patients, and quantification of the percentage of p16^INK4a positive FLSs (n  =  25 Nor, n  =  33 OA). Scale bar: 100 µm. c Spearman’s correlation analysis was performed between Mankin score and the percentage of p16^INK4a positive FLSs in OA samples (n  =  33). d Quantitative PCR analysis of CDKN1A and CDKN2A in FLSs. (n  =  25 Nor, n  =  33 OA). e Western blotting analysis of senescent markers. n = 3 independent biological replicates. f Representative images of SA-β-Gal staining for Nor-FLSs and OA-FLSs. n  =  9 independent biological replicates. Scale bar: 100 µm. g Representative images of immunofluorescence staining of p16^INK4a in Nor-FLSs and OA-FLSs, and the percentage of p16^INK4a positive cells. n  =  15 independent biological replicates. Scale bar: 50 µm. h Quantitative PCR analysis (n  =  3 independent biological replicates) and Elisa assay (n  =  6 independent biological replicates) of pro-inflammatory cytokine (IL-1β and TNF-α) in Nor-FLSs and OA-FLSs. i Western blotting assay to detect the protein levels of chondrocytes co-cultured with Nor-FLSs or OA-FLSs. n = 3 independent biological replicates. j Representative images of Safranin O/Fast green staining of knee joints. n  =  10. Scale bar: 200 µm. k Representative images of immunohistochemistry staining of p16^INK4a. n  =  10. Scale bar: 100 µm. l The severity of the OA phenotype was assessed using the OARSI score system. n = 10 independent biological animals. m Representative images of immunofluorescence in knee joints. S, synovium; C, cartilage. Scale bar: 500 µm (Left panel), 50 µm (Right panel). n Quantification of the percentage of p16^INK4a positive FLSs in the synovium of mice. n  =  10 independent biological animals. o Spearman’s correlation analysis was performed between OARSI score and the percentage of p16^INK4a positive FLSs in OA mice. n  =  10. All data were presented as the means ± SD. P values were determined by two-tailed unpaired Student’s t-test. P < 0.05 was considered statistically significant. Source data are provided as a Source Data file.