29-kDa FN-f induces pro-inflammatory cytokine expressions via the cGAS/STING/IRF3 signaling pathways. (A) Blockade of cGAS or STING inhibited 29-kDa FN-f-induced activation of TBK1 and IRF3. Chondrocytes were transfected with si-cGAS or si-STING and incubated with 29-kDa FN-f for 24 h. Levels of phosphorylated TBK1, IRF3 and IκBα were measured by western blot analysis. Western blot data are representative of three independent experiments from different donors. β-actin served as a loading control. (B) The 29-kDa FN-f-stimulated expression of GM-CSF, G-CSF, and IFN-α was decreased by silencing cGAS or STING. Chondrocytes were transfected with si-cGAS or si-STING and incubated with 29-kDa FN-f for 6 h. The expression of CSFs and IFN-α was measured using qRT-PCR analysis. GAPDH was used as an endogenous control. Data are presented as the mean ± standard deviation (SD) of duplicate data obtained from four different donors. *P < 0.05, **P < 0.01, ***P < 0.001 vs. si-control-transfected cells.