IL-1β and IL-17 Stimulation of Pro-inflammatory Molecules in TMJ Fibroblasts

Objectives: Interleukin-1β (IL-1β) and IL-17 are elevated in synovial fluid from TMJ with osteoarthritis (OA) and regulate pro-inflammatory IL-6 and IL-8, and vascular endothelial growth factor (VEGF), which attracts osteoclasts and induces MMPs. TMJ synovial fibroblast-like cells produce extracellular matrix molecules, inflammatory mediators, and MMPs which degrade the TMJ. IL-17 may act synergistically with IL-1β to upregulate production of inflammatory mediators. Objectives: determine production and regulation of IL-6, IL-8, and VEGF by human TMJ synovial fibroblast-like cells in response to IL-1β, IL-17, or both.
Methods: Synovial fibroblast-like cell lines from human TMJ with OA (SF3, SF4) and ankylosed human TMJ without degeneration (NSF) were used. Cells were incubated ± IL-1β (0.01 nM), IL-17 (0.5-100 ng/ml), or both, in serum-free medium for 1-6d. IL-6, IL-8 and VEGF were measured in cell supernatants by ELISA. Data analysis: ANOVA and Scheffe’s F procedure.
Results: IL-17 did not significantly increase VEGF production and caused small (≤2-fold) increases at d6 in IL-6 and IL-8 in one cell line only, at ≥50 ng/ml. IL-1β was a much stronger stimulant of IL-6 (~10 - >5000-fold), IL-8 (~10 - ~200-fold) and to a lesser extent VEGF (~2 - ~8-fold) (p<0.003). With IL-1β, IL-17 synergistically stimulated IL-6>>>IL-8>>VEGF in SF3 (p≤0.003), and IL-6 in SF4 (p<0.007). IL-17 had neither additive nor synergistic effects on production of any of the cytokines in NSF, or IL-8 and VEGF in SF4.
Conclusions: Results are consistent with other studies showing weak activation by IL-17 compared to IL-1β and synergistic effects with other cytokines. Identification of major stimulants of specific pro-inflammatory molecules by synovial fibroblasts and other TMJ cells, and means of inhibition, are important in developing non-conventional therapies for severe cases of TMJ inflammatory disorders.