Fig. 1

NOD2 is upregulated in synovial macrophages of osteoarthritis patients. A Volcano plot demonstrating differentially expressed genes in macrophages stimulated by HMGB1 for 4 h. B Heat map and cluster analysis of RNA-seq data. C Protein–protein interaction network indicating the association of NOD2 with HMGB1/TLR4 signaling. D Expression of NOD2 and TNF-α in osteoarthritic synovial tissue compared with non-osteoarthritic tissue (scale bar = 100 μm). E Intensity score of NOD2 and TNF-α in osteoarthritic synovial tissue compared with non-osteoarthritic synovial tissue. F Co-localization of NOD2 with F4/80, a macrophage marker (scale bar = 200 μm). G, H M1/M2 ratio favoring M1 subtype transformation in osteoarthritis synovial tissue. I Elevated mRNA expression of NOD2 and TNF-α in osteoarthritic synovial tissue. J Elevated expression of NOD2 and TNF-α at protein level in osteoarthritic synovial tissue. *p < 0.05, **p < 0.01, and ***p < 0.001. Data were presented as boxplots (center line, median; box limits, 25 to 75th percentiles; whiskers, min to max), or mean ± s.e.m. values. n = 3 biologically independent replicates for PCR. Kruskal–Wallis test followed by Dunn’s multiple comparisons test for ODS scores of IHC images and Student’s t test for PCR