Regulation of Synovial Inflammation and Tissue Destruction by Guanylate Binding Protein 5 in Synovial Fibroblasts From Patients With Rheumatoid Arthritis and Rats With Adjuvant‐Induced Arthritis

OBJECTIVE Rheumatoid arthritis synovial fibroblasts (RASFs) are crucial mediators of synovial inflammation and joint destruction. However, their intrinsic immunoregulatory mechanisms under chronic inflammation remain unclear. Thus, present study was aimed to understand the role of newly identified GTPase, guanylate-binding protein 5 (GBP5) in RA pathogenesis. METHODS The expression of GBP1-GBP7 transcripts was evaluated using qRT-PCR in RA synovial tissues (RASTs) or non-diseased STs (NLSTs). Transient siRNA knockdown and lentiviral overexpression studies in human RASFs examined the regulatory role of GBP5 on proinflammatory cytokine signaling pathways. Unbiased whole transcriptome RNA-sequencing analysis examined the impact of GBP5 on RASF molecular functions. These findings were confirmed using in vivo rat model of adjuvant-induced arthritis (AIA). RESULTS Among different GBPs evaluated, GBP5 was selectively upregulated in RASTs (p<0.05; n=4) and the joints of AIA rats (p<0.05; n=6), and was significantly induced in human RASFs by IL-1β, TNF-α and/or IFN-γ (p<0.05; n=3). Bioinformatics analysis of RNA-sequencing data identified cytokine-cytokine receptor signaling as a major function altered by GBP5, with IL-6 signaling as a primary target. Knockdown of GBP5 amplified IL-1β-induced IL-6, IL-8, ENA-78/ CXCL5 by 44%, 54%, 45%, respectively, and MMP-1 production by several-folds, effects which reversed with exogenously delivered GBP5. Lack of GBP5 increased IFN-γ-induced proliferation and migration in human RASFs. In vivo GBP5 knockdown using intra-articular siRNA exacerbated disease onset, severity, synovitis, and bone destruction in AIA. CONCLUSION Expressed by RASFs in response to cytokine stimulation, GBP5 has potential to restore cellular homeostasis and blunt inflammation and tissue destruction in RA.