DJ-1 controls T cell differentiation and osteoclastogenesis in rheumatoid arthritis

Herein, we investigated the effect of DJ-1 on helper T cell differentiation, fibroblast-like synoviocyte (FLS) activation, and osteoclastogenesis in rheumatoid arthritis (RA). Serum and synovial fluid (SF) of RA and osteoarthritis (OA) patients were collected, and DJ-1 and H(2)O(2) levels were investigated. CD4(+) cells from peripheral blood mononuclear cells (PBMCs) were cultured under type 17 helper T cell (Th17) polarization conditions, and CD4(+) T cell differentiation, pro-inflammatory cytokine levels, and soluble receptor activator of nuclear factor kappa-Β ligand (RANKL) were assessed. RA-FLSs were stimulated with 50 μM H(2)O(2), and DJ-1 (10, 50, 100 ng/mL) to evaluate MMP-9, VEGF, TNF-α, and sRANKL production, while RANKL(+) FLSs were assessed using flow cytometry. Monocytes were cultured with RANKL or IL-17A with or without DJ-1 and H(2)O(2)-pretreated RA-FLS, and tartrate-resistant acid phosphatase (TRAP) staining and RT-qPCR of osteoclast-related genes were performed. The levels of DJ-1 and H(2)O(2) in serum and SF of RA patients were higher than those of OA patients. Under Th17-polarizing conditions, CD4(+)RANKL(+) and CD4(+)CCR4(+)CCR6(+)CXCR3(-) T cells decreased, whereas CD4(+)CD25(high)Foxp3(+) T cell increased after DJ-1 administration. Additionally, IL-17A, TNF-α, and sRANKL levels decreased in DJ-1-treated groups. DJ-1 lowered MMP-9, VEGF, TNF-α, and sRANKL levels, and RANKL(+) FLS in ROS-stimulated RA-FLS. Both RANKL and IL-17A stimulated osteoclast differentiation, DJ-1 decreased TRAP(+) cell count, and the expression levels of TRAP, ATP6v0d2, NFATc1, and CTSK. These findings were also observed in in vitro osteoclastogenesis with DJ-1 pretreated RA-FLS. As DJ-1 regulates Th17/Treg imbalance, pro-inflammatory cytokine production, RA-FLS activation, and osteoclastogenesis, it holds potential for RA therapy.