Exposure to monosodium urate (MSU) crystals induces the expression of transglutaminase 2 (TG2) in synovial tissues of patients with gouty arthritis (GA).
(A) RT-PCR analysis of TG2 mRNA expression in synovial fluid mononuclear cells (SFMCs) from six patients with GA, one patient with rheumatoid arthritis (RA) and one with normal PBMCs (N). (B) mRNA levels of TG2 in SFMCs of patients with gouty arthritis (GA) (n = 16), osteoarthritis (OA) (n = 20), rheumatoid arthritis (RA) (n = 5) and in PBMCs of healthy donors (normal) (n = 5). Each point represents an individual patient. TG2 mRNA levels are expressed in arbitrary units (horizontal lines denote median values). (C) Representative images of immunohistochemical staining of TG2 in healthy tissue (left panel), osteoarthritis (OA) (middle panel) and GA (right panel) synovial tissues. Strong staining for TG2 was observed in the inflammatory cell infiltrate in GA synovium (Original magnification × 200). (D-E) PBMCs (D) and MDMs (E) isolated from healthy donors were stimulated with or without MSU crystals (1 mg/ml) for 0-12 h, and TG2 mRNA expression was analyzed by RT-PCR. (F) Induction of IL-1β, TNF-α, TG2 and TGF-β1 mRNA expression in RAW264.7 cells stimulated with MSU crystals (0.1-1.0 mg/ml) for 4 h analyzed by RT-PCR. (G) Western blot analysis of TG2 expression in whole-cell lysates from RAW264.7 cells stimulated for 24 h with increasing concentrations MSU crystals (0.1-1.0 mg/ml) and for the indicated time periods with 1 mg/ml MSU crystals. The ‘Fold’ induction was measured by densitometry analysis and normalized to β-actin. (H) Cells were stimulated with or without MSU crystals (1 mg/ml). The levels of IL-1β, TNF-α and TGF-β1 in supernatants were evaluated by ELISA at the indicated time points. The results are expressed as the means ± SEM from three independent experiments (n ≧ 3, * = P < 0.05, ** = P < 0.01 compared with control (100%)).