TNF-α Regulated Bidirectional Interaction Between Bone Marrow Mesenchymal Stem Cells and Articular Chondrocytes.

Background: Articular chondrocytes (ACs) secrete a variety of extracellular matrix components to maintain the functions of articular cartilage. Degeneration of ACs leads to the degeneration of articular cartilage and consequently to osteoarthritis. The secretion of bone marrow mesenchymal stem cells (BMSCs) is capable of protecting ACs from degeneration, and thus BMSCs are widely applied to treat osteoarthritis.

Objective: This study aims to explore whether BMSCs and ACs will affect the functions of each other through their secretions in the context of osteoarthritis.

Design: BMSCs and ACs isolated from rabbits were identified using flow cytometry and immunocytochemistry. Conditioned medium of BMSCs and ACs treated with 0, 5, 10, 20, and 40 ng/ml of tumor necrosis factor-alpha (TNF-α) were collected and used to treat ACs and BMSCs, respectively. The viabilities of ACs and BMSCs treated with condition medium were assessed using a Cell Count Kit-8 (CCK-8) kit. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR), immunoblotting, and enzyme-linked immunosorbent assay (ELISA) methods were employed to evaluate the relative expression levels of genes and proteins, as well as the cytokine concentrations in the supernatant.

Results: Immunofluorescence and flow cytometry results indicated that the purity of isolated cells exceeded 95%. CCK-8 analysis showed that 6 hours of treatment with a conditioned medium did not affect the viability of BMSCs and ACs. However, treatment for 12 hours or longer significantly increased the viability of BMSCs (p < 0.05) and significantly decreased the viability of ACs (p < 0.01). RT-qPCR results demonstrated that the relative expression levels of Runx2 (1.15-3.91), Alp (1.06-2.84), TNF (BMSCs: 0.94-2.54; ACs: 1.03-2.64), IL6 (BMSCs: 0.98-2.78; ACs: 0.96-3.71), IL17A (BMSCs: 1.08-5.91; ACs: 0.90-4.20), and IL10 (BMSCs: 0.93-2.82; ACs: 0.89-2.25) genes in conditioned medium-treated BMSCs and ACs were dose-dependently elevated (p < 0.001) by TNF-α treatment. Immunoblotting analysis revealed that the expression levels of RUNX2 (0.53-0.86) and ALP (0.49-0.85) proteins were also dose-dependently elevated (p < 0.001) by TNF-α treatment. ELISA results showed similar TNF-α dose-dependent increases (p < 0.001) in the supernatant concentrations of pro-inflammatory cytokines TNF-α (BMSCs: 36.90 ± 0.75 to 199.38 pg/ml; ACs: 29.76 to 293.99 pg/ml), interleukin (IL)-6 (BMSCs: 4.96-48.24 pg/ml; ACs: 6.12-38.15 pg/ml), IL-17 (BMSCs: 3.06-28.99 pg/ml; ACs: 3.08-28.51 pg/ml), as well as the anti-inflammatory cytokine IL-10 (BMSCs: 6.34-65.02 pg/ml; ACs: 5.30-34.85 pg/ml).

Conclusion: Together, these results indicate a TNF-α-regulated bidirectional interaction between BMSCs and ACs, deepening our understanding of the pathogenesis of osteoarthritis and aiding in its prevention and treatment.