IL-6 trans-signaling activates the TGF-β pathway via soluble factors in difficult-to-treat rheumatoid arthritis joint fluid.

OBJECTIVE

To explore the impact of joint fluid (JF) from difficult-to-treat (D2T)rheumatoid arthritis (RA) patients on joint inflammation.

METHODS

We compared the clinical characteristics of D2T RA and non-D2T RA patients. Joint fluid samples from patients with various forms of chronic arthritis were analyzed. The activation of IL-6/STAT3 and TGF-β/SMAD3 pathways in normal Fibroblast-like synoviocytes (FLS) after exposure to D2T RA joint fluid was also evaluated, along with the effects of pathway inhibitors on cell proliferation, apoptosis, invasion, and migration.

RESULTS

D2T RA joint fluid showed elevated levels of IL-6 and TGF-β1 compared to non-D2T RA, osteoarthritis, and ankylosing spondylitis samples. The IL-6/STAT3 pathway was directly activated in normal FLS upon exposure to D2T RA joint fluid, while the TGF-β/SMAD3 pathway was indirectly activated through IL-6 trans-signaling, resulting in increased proliferation, migration, invasion, and anti-apoptotic properties of FLS. The use of SMAD3 Inhibitory Selective 3 (SIS3) to block the TGF-β/SMAD3 pathway partially mitigated the effects of D2T RA joint fluid. Tocilizumab and the soluble glycoprotein 130 Fc fusion protein (sgp130Fc) successfully inhibited IL-6-associated pSMAD3 activation, highlighting a mediating role of IL-6.

CONCLUSION

The joint fluid milieu may contribute to persistent synovial activation in D2T RA, and highlights IL-6 trans-signaling as a potential therapeutic target in this context. In addition, timely aspiration of joint fluid from patients with D2T RA may help modulate the local inflammatory microenvironment and could represent a supportive strategy in disease management.