CXCL16 upregulates RANKL expression in rheumatoid arthritis synovial fibroblasts through the JAK2/STAT3 and p38/MAPK signaling pathway

Objective To explore the influence of chemokine, CXCL16, on the expression of the receptor activator nuclear factor kappa B ligand (RANKL) in rheumatoid arthritis (RA) fibroblast-like synoviocytes (RA-FLS). Methods The expression of CXCL16/CXCR6 and RANKL in RA or osteoarthritis (OA) patient synovia was examined by Western blot and immunohistochemistry. The serum concentration of CXCL16 and RANKL was measured by enzyme-linked immunosorbent assay (ELISA). RA-FLS were treated with recombinant CXCL16, and RANKL mRNA and protein were measured using PCR, Western blot and ELISA. Results The synovial expression of CXCL16, CXCR6, and RANKL was higher in RA patients than in patients with OA. The serum CXCL16 and RANKL levels were higher in RA patients compared with OA patients and healthy controls. CXCL16 correlated with erythrocyte sedimentation rate, C reactive protein, disease activity, serum rheumatoid factor, and RANKL. RA-FLS treated with CXCL16 showed markedly increased expression of RANKL. When STAT3 or p38 activation was blocked by an inhibitor, CXCL16 failed to upregulate RANKL expression. In contrast, inhibiting the Akt or Erk pathway did not achieve the same effect. Conclusions CXCL16 upregulates RANKL expression in RA-FLS and these effects are mainly mediated by the JAK2/STAT3 and p38/MAPK signaling pathways.