Disorders in angiogenesis and redox pathways are main factors contributing to the progression of rheumatoid arthritis: a comparative proteomics study

Objective: To clarify the pathogenesis of rheumatoid arthritis (RA) by comparing protein expression in fibroblast-like synoviocytes (FLS) from patients with RA with that in FLS from normal subjects, using proteomics analysis.

Methods: Proteins extracted from primary cultures of FLS obtained from 50 patients with RA and 10 normal subjects were analyzed by automated 2-dimensional nano-electrospray ionization liquid chromatography tandem mass spectometry. Differentially expressed proteins were screened by 2-sample t-test (P < 0.05) and fold change (>1.5), based on the bioinformatics analysis. The expression of vasculature development-related proteins (Thy-1, connective tissue growth factor [CTGF], and thrombospondin 1 [TSP-1]) and redox-related proteins (superoxide dismutase 2 [SOD2]) in synovial tissue was confirmed by real-time polymerase chain reaction and Western blotting. The effect of Thy-1 and CTGF knockdown on Thy-1, CTGF, TSP-1, and vascular endothelial growth factor (VEGF) was analyzed by RNA interference experiments.

Results: According to the criteria of having >1 unique peptide per protein present and a false discovery rate of ≤5%, 1,060 proteins were identified from patients with RA, and 1,292 proteins were identified from normal subjects, from which 100 differentially expressed proteins were screened out from the RA proteins. Of these, 46 proteins were up-regulated, and the remaining 54 proteins were down-regulated. Gene ontology and pathway analyses showed that 6 vasculature development-related proteins were up-regulated, including Thy-1, CTGF, and TSP-1, while 11 redox-related proteins were down-regulated, including SOD2. The results were consistent with those obtained using mass spectrometry. Thy-1, VEGF, CTGF, and TSP-1 were down-regulated after Thy-1 knockdown, and VEGF and CTGF were down-regulated after CTGF knockdown. Recombinant human CTGF could enhance proliferation and Transwell migration of human umbilical vein endothelial cells.

Conclusion: Up-regulation of vasculature development-related proteins and down-regulation of redox-related proteins in FLS are predominant factors that may contribute to the pathogenesis of RA.