Background/Purpose: Guanylate binding protein 5 (GBP5), an interferon gamma (IFN-γ) inducible protein, helps to defend against invading pathogens. However, its role and properties beyond anti-viral or anti-bacterial action remains unknown. In the present study, we evaluated the role of GBP5 and its corroboration with IFN-γ in regulating rheumatoid arthritis synovial fibroblast (RASF) mediated inflammation and tissue destruction.

Methods: Cell lysates from RASFs and non-diseased SFs (NLSFs) were prepared to evaluate the expression levels of GBP5 using Western immunoblotting and qRT-PCR methods. siRNA mediated knockdown of GBP5 was conducted to study its effect on IFN-γ (10 ng/ml), IL-1β (10 ng/ml) and/or TNF-α (20 ng/ml)-induced downstream signaling pathway in RASFs. Conditioned media was used to quantitate IL-6, IL-8, matrix metalloproteinase-1 (MMP-1), and CXCL5 production by ELISA. The lentiviral delivery method was used to overexpress GBP5 to evaluate its potential regulatory effects in RASFs.

Results: Our Western blot analysis showed that the expression of GBP5 is significantly reduced in RASFs compared to NLSFs (p<0.05; n=6). We observed a higher expression of GBP5 upon IFN-γ stimulation and the expression was further augmented with IL-1β stimulation (p<0.05; n=6). Co-treatment of RASFs with IFN-γ significantly downregulated IL-1β-induced IL-6, IL-8, and MMP-1 production in RASFs (p<0.05; n=3). To our surprise, siRNA-mediated knockdown of GBP5 reduced the inhibitory potential of IFN-γ and resulted in further upregulation of IL-1β-induced IL-6, IL-8, MMP-1, and CXCL5 production by 84%, 66%, 8-fold, and 72%, respectively (p<0.05; n=3). Evaluating the impact of GBP5 knockdown on the RASF signaling pathways, we observed that GBP5 knockdown in human RASFs selectively amplified the constitutive as well as IL-1β-induced phosphorylation of ERK1/2 and JNK mitogen-activated protein kinases, which are important mediators of inflammation and tissue destruction in RA. Intriguingly, lentivirus-mediated restoration of GBP5 abrogated IL-1β-induced proinflammatory cytokine production, suggesting that GBP5 plays an anti-inflammatory role by inhibiting RASF mediated inflammation.

Conclusion: Our findings suggest that the lack of GBP5 contributes to synovial inflammation, and its restoration suppresses RASF-mediated inflammation and tissue destruction.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/guanylate-binding-protein-5-gbp5-inhibits-rheumatoid-arthritis-synovial-fibroblast-mediated-inflammation-and-tissue-destruction/