Protective Role of Optineurin Against Joint Destruction in Rheumatoid Arthritis Synovial Fibroblasts

Objective Optineurin ( OPTN ) is an autophagy adaptor/receptor that acts as an intrinsic negative regulator of osteoclast differentiation. RANKL expressed by rheumatoid arthritis synovial fibroblasts ( RASF s) is primarily responsible for the development of bone erosions in patients with RA . The aim of the present study was to explore the role of OPTN in the pathogenesis of joint destruction in RA . Methods RASF s were left untreated or incubated with tumor necrosis factor ( TNF ) or interferon‐γ ( IFN γ), and expression of OPTN by RASF s was analyzed by reverse transcription–quantitative polymerase chain reaction ( RT ‐ qPCR ) and Western blotting. Expression of RANKL and osteoprotegerin ( OPG ) was evaluated in cultures of OPTN ‐reduced RASF s with or without TNF or IFN γ treatment. OPTN ‐reduced RASF s were cocultured with monocytes and stained for tartrate‐resistant acid phosphatase ( TRAP ). IκBα, NF ‐κB1, and RelA protein levels were measured to evaluate NF ‐κB signaling. Expression of messenger RNA ( mRNA ) for matrix metalloproteinase 3 ( MMP 3 ), interleukin‐6 ( IL 6 ), GATA binding protein 3 ( GATA 3 ), carbohydrate sulfotransferase 15 ( CHST 15 ), hyaluronan synthase 1 ( HAS 1 ), and GATA 1 was analyzed by RT ‐ qPCR . Results In RASF s incubated with TNF or IFN γ, OPTN expression was up‐regulated and RANKL expression was increased, and these effects were further pronounced in OPTN ‐reduced RASF s (all P < 0.05 versus controls). OPG mRNA levels remained unchanged. Monocytes cocultured with OPTN ‐reduced RASF s differentiated to a greater extent into TRAP + multinucleated cells compared to monocytes cocultured with control RASF s ( P < 0.05). IκBα degradation and nuclear NF ‐κB1 expression following TNF treatment were both prolonged in OPTN ‐reduced RASF s (each P < 0.05 versus controls). MMP 3 mRNA levels were up‐regulated, while GATA 3 , CHST 15 , and HAS 1 mRNA levels were down‐regulated in OPTN ‐reduced RASF s (each P < 0.05 versus controls). Conclusion OPTN plays a protective role in RA when it is up‐regulated in RASF s in the presence of proinflammatory cytokines. Absence of OPTN might worsen RA by generating a joint‐destructive state, as indicated by evidence of increased RANKL expression on RASF s and subsequent osteoclast differentiation.