MASARU KATO, Japan
Hokkaido University Department of Rheumatology, Endocrinology and NephrologyPresenter of 1 Presentation
OPTINEURIN IN SYNOVIAL FIBROBLASTS PROTECT THE JOINT DESTRUCTION BY SUPPRESSING OSTEOCLASTOGENESIS IN RHEUMATOID ARTHRITIS
Abstract
Background and Aims
Optineurin (OPTN) is an autophagy receptor with multiple properties and has been reported to act as a negative regulator of osteoclastogenesis in osteoclast precursors. Since RANKL expressed on synovial fibroblasts (SFs) plays a major role in osteoclastogenesis in rheumatoid arthritis (RA) joint, we aimed to explore the role of OPTN in SFs form RA patients (RASFs).
Methods
The expression of OPTN was analyzed in RASFs using RT-qPCR and western blot. Cell surface expression of RANKL was analyzed by flow cytometry. OPTN was downregulated in RASFs using siRNA. Monocytes were cocultured with OPTN-reduced RASFs and stained with Tartrate-Resistant Acid Phosphatase (TRAP) to evaluate osteoclast differentiation. Protein levels of IκBα and nuclear NF-κB1 were measured to evaluate NF-κB signaling.
Results
OPTN was upregulated by TNF-α or IFN-γ in RASFs at both mRNA and protein levels. Cell surface RANKL was significantly increased following treatment with TNF-α or IFN-γ and the effect was further pronounced in OPTN-reduced RASFs compared to control RASFs, while osteoprotegerin levels remained unchanged after OPTN knockdown. Monocytes cocultured with OPTN-reduced RASFs differentiated more into TRAP+ multinucleated cells compared to those cocultured with control RASFs. MMP3 and IL-6 were upregulated while GATA-3, CHST15 and HAS1 were downregulated in OPTN-reduced RASFs. IκBα degradation and nuclear NF-κB1 expression following TNF-α treatment was prolonged in OPTN-reduced RASFs.
Conclusions
OPTN plays a protective role in RA with its upregulation when immersing with pro-inflammatory cytokines. Absence of OPTN might worsen RA by generating joint destructive state including increased RANKL expression on RASFs and subsequent osteoclast differentiation.