OP0081 IL-13 REDUCES BONE EROSION IN RHEUMATOID ARTHRITIS BY UP-REGULATING OPG IN SYNOVIAL FIBROBLASTS

Abstract

BackgroundBone erosion in rheumatoid arthritis (RA) is partly caused by excessive activation of osteoclasts[1]. Osteoclasts can be derived from RA synovium and their differentiation can be inhibited by OPG, a decoy receptor of the osteoclastogenesis promoting cytokine RANKL[2,3]. Fibroblast-like synoviocytes (FLSs) are a main type of stromal cells in the synovium that can secret OPG[4]. The OPG secretion by FLSs can be modulated by various cytokines[5]. Interleukin (IL)-13 is a cytokine rich in early RA synovial fluid and it decreases as RA progresses[6]. IL-13 was reported to alleviate bone erosion in RA mouse models[7]. However, how IL-13 reduces bone destruction remains unclear.ObjectivesTo investigate if IL-13 can inhibit osteoclast differentiation by up-regulating OPG in FLSs of RA patients (RA-FLSs), thus reduces bone erosion in RA.MethodsFLSs were isolated from the synovium tissue of RA patients with informed consent who underwent joint replacement surgery (Ethics No. 2021-544-01). OPG and RANKL expression by RA-FLSs were evaluated by qRT-PCR. OPG secretion was determined by ELISA. Western blot was performed to analyze OPG expression and the activation of STAT6 pathway. IL-13 and OPG siRNA pre-treated RA-FLSs conditioned medium were used in osteoclast induction to test if IL-13 can inhibit osteoclastogenesis by up-regulating OPG in RA-FLSs. Micro-CT scanning and immunofluorescence were done to determine if IL-13 can induce OPG expression and alleviate bone erosion in vivo.ResultsIL-13 can significantly upregulate OPG expression and secretion by RA-FLSs. Meanwhile, RANKL/OPG ratio was downregulated (Figure 1A). STAT6 phosphorylation and OPG upregulation of RA-FLSs by IL-13 can be significantly inhibited by a STAT6 inhibitor (inh.) (Figure 1B). IL-13 receptor α1 (IL-13Rα1) and IL-13 receptor α2 (IL-13Rα2) knockdown can inhibit OPG upregulation by IL-13 in RA-FLSs, indicating that IL-13 can induce OPG secretion in RA-FLSs through IL-13Rα1 and IL-13Rα2 via STAT6 pathway (Figure 1C). 20% conditioned medium of RA-FLSs pretreated by IL-13 can significantly inhibited osteoclast differentiation in vitro. OPG knockdown in RA-FLSs significantly reversed the inhibition, indicating that IL-13 inhibits osteoclastogenesis by upregulating OPG in RA-FLSs (Figure 1D). In collagen-induced arthritis mice, IL-13 injection can reduce bone destruction in the ankle joint. Meanwhile, OPG expression in vemintin positive FLSs was increased (Figure 1E and F).Figure 1.ConclusionIL-13 can inhibit osteoclastogenesis by up-regulating OPG in RA-FLSs through IL-13 receptors via STAT6 pathway, thus ameliorate bone erosion in RA.