Role Of Adiponectin In Collagen-Induced Arthritis

Objectives Rheumatoid arthritis(RA), a common human autoimmune disease,affects multiple joints and eventually cause joint damage. However, the pathogenesis of RA still remains unclear. Adiponectin (AD), a recently discovered protein secreted by adipose tissue, plays an important role in the regulation of inflammation and bone metabolism. Our previous study found that AD was significantly higher expression in RA serum, synovial fluid and peripheral blood mononuclear cells.This study aimed to investigate the role of adiponectin in pathogenesis of RA.Methods (1) To construct the type 2 recombinant adeno-associated virus vector encoding the gene of AD (rAAV2-AD). (2) The rat synovial fibroblasts were transfected with rAAV2-AD vectors at different multiplicity of infection (MOI). The mRNA levels of AD, interleukin-1β(IL-1β), interleukin -6 (IL-6), tumor necrosis factor-α(TNF-α) and B cell stimulating factor (BAFF) expression were detected by real-time PCR after 7d. (3) To establish type II collagen-induced arthritis in rat. Upon the 2nd immunization with collagen, knee joints of CIA rats were injected with rAAV2-AD in the periarticular regions. The arthritis onset, diameters of swollen ankle joints and volume of inflamed claws were examined regularly. Levels of IL-1βand IL-6 production were detected by ELISA. At the 8th week, synovial membrane of the left knee joint from sacrificed rats was prepared for RNA extraction and detection of AD,IL-6, TNF-αand BAFF expression by real-time PCR whereas the right knee for Micro-CT and pathological examination.Results (1) Recombinant rAAV2-AD was successfully constructed. (2) In cultured synovial fibroblasts, high level of adiponetin was detected in transfected cells. The mRNA expression of IL-6, TNF-αand BAFF in different MOI group was significantly different(P<0.05 or P<0.01),and the highest in the group of MOI=5×10^5v.g./cell(P<0.01). (2) Collagen induced arthritis model was successfully established. Compared with the control group, 14d after immunization, the ankles and toes of collagen-induced rats showed severe swelling with significantly increased arthritis index(P<0.05). After the injection of rAAV-AD, AD successfully induced expression in the joints. As detected by ELISA, serum levels of IL-1βand IL-6 expression in the normal group and the CIA showed a significant difference(P<0.01). However, in the 3th week after joint injection, there was some modest increase between the rAAV-AD articular injection group and other two CIA model groups(P<0.05), and obviously higher than the normal group(P<0.01). Real-time PCR assay detected significantly higher levels of AD,IL-6, TNF-αand BAFF expression in rAAV2-AD injection group(P<0.01). Micro-CT and pathologic analysis revealed more sever articular surface damage in rAAV2-AD injected group than in the rAAV2-EGFP injected group.Conclusions (1) Adiponectin in synovial fibroblasts can promote the expression of inflammatory cytokines TNF-α, IL-6 gene and BAFF gene mRNA, indicating that adiponectin may promote the secretion of inflammatory cytokinesis in synovial fibroblasts and involve in B cells activation. (2) Although increased expression of AD by intra-articular injection has a little significant effect on systemic inflammation, there were significantly increased joint inflammation and bone erosion in the articular surface in CIA rats injected with rAAV2-AD vectors, suggesting that AD may be involved in the inflammation and bone destruction in RA.