Chondrocyte-specific STAT3 knockout attenuates osteoarthritis progression via inflammation regulation

Objective: To investigate the role and mechanism of chondrocyte-specific knockout of signal transducer and activator of transcription 3 (STAT3) in medial meniscus instability (DMM)-induced osteoarthritis (OA) in mice. Methods: A tamoxifen-induced conditional knockout (cKO) mouse model (COL-II-Cre ⁺ /STAT3 ^flox/flox ) was established, and OA was induced by DMM surgery. Littermate (STAT3 ^flox/flox ) mice served as controls. Samples were collected at 4 and 8 weeks post-surgery. Cartilage pathology was evaluated using safranin-O-green staining and Mankin scoring. Subchondral bone changes were assessed by micro-computed tomography (CT). Enzyme-linked immunosorbent assay (ELISA) was performed to determine the serum interleukin (IL)-1b, IL-6, and tumor necrosis factor-alpha (TNF-α). Immunohistochemistry was performed to detect Aggrecan, COL-II, STAT3, p-STAT3, IL-6, TNF-α, matrix metalloproteinase-13 (MMP13), and A Disintegrin And Metalloproteinase with Thrombospondin motifs-4 (ADAMTS-4) expressions in the cartilage. Gene expression was analyzed using quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). For in vitro studies, primary chondrocytes from control mice were transduced with Cre recombinase to generate STAT3-deficient cells and stimulated with IL-1β to establish an OA model. The gene and protein expression were examined by qRT-PCR and Western blotting. Results: Compared with control DMM mice, cKO-DMM mice exhibited significantly reduced cartilage degeneration and lower serum levels of IL-1β, IL-6, and TNF-α ( P < 0.05). In cartilage tissues, cKO-DMM mice showed increased COL-II and Aggrecan expression, along with downregulation of IL-1β, IL-6, TNF-α, MMP13, ADAMTS-4, JAK2, and the p-STAT3/STAT3 ratio ( P < 0.05). Chondrocyte apoptosis was also reduced. Micro-CT analysis demonstrated that STAT3 knockout attenuated subchondral osteosclerosis at 8 weeks post-DMM, with significant reductions in BV/TV and BMD ( P < 0.001). In vitro, STAT3 deletion alleviated IL-1β–induced COL-II and Aggrecan loss, while suppressing IL-6, TNF-α, and JAK2/STAT3 pathway activation ( P < 0.05). Conclusion: Chondrocyte-specific STAT3 knockout effectively mitigates DMM-induced OA progression in mice. The protective mechanism involves suppression of inflammatory cytokine release, downregulation of MMP13/ADAMTS-4 and JAK2/STAT3 signaling, and the preservation of cartilage integrity.