Genome-wide gene expression was comparatively investigated in early-passage
rheumatoid arthritis (RA) and
osteoarthritis (OA) synovial fibroblasts (
SFBs; n = 6 each) using
oligonucleotide microarrays;
mRNA/
protein data were validated by quantitative PCR (qPCR) and western blotting and immunohistochemistry, respectively. Gene set enrichment analysis (GSEA) of the microarray data suggested constitutive upregulation of components of the
transforming growth factor (
TGF)-beta pathway in RA
SFBs, with 2 hits in the top 30 regulated pathways. The
growth factor TGF-beta1, its receptor
TGFBR1, the
TGF-beta binding proteins LTBP1/2, the
TGF-beta-releasing
thrombospondin 1 (THBS1), the negative effector SkiL, and the smad-associated molecule SARA were upregulated in RA
SFBs compared to OA
SFBs, whereas
TGF-beta2 was downregulated. Upregulation of
TGF-beta1 and THBS1
mRNA (both positively correlated with
clinical markers of disease activity/severity) and downregulation of
TGF-beta2 mRNA in RA
SFBs were confirmed by qPCR.
TGFBR1 mRNA (only numerically upregulated in RA
SFBs) and SkiL
mRNA were not differentially expressed. At the
protein level,
TGF-beta1 showed a slightly higher expression, and the signal-transducing
TGFBR1 and the
TGF-beta-activating THBS1 a significantly higher expression in RA
SFBs than in OA
SFBs. Consistent with the upregulated
TGF-beta pathway in RA
SFBs, stimulation with
TGF-beta1 resulted in a significantly enhanced expression of
matrix-metalloproteinase (MMP)-11
mRNA and
protein in RA
SFBs, but not in OA
SFBs. In conclusion, RA
SFBs show broad, constitutive alterations of the
TGF-beta pathway. The abundance of
TGF-beta, in conjunction with an augmented
mRNA and/or
protein expression of
TGF-beta-releasing THBS1 and
TGFBR1, suggests a pathogenetic role of
TGF-beta-induced effects on
SFBs in RA, for example, the augmentation of
MMP-mediated matrix degradation/remodeling.