OBJECTIVE: MicroRNA (miRNA) are recognized as important regulators of a variety 
of fundamental biologic processes. Previously, we described increased expression 
of miR-155 and miR-146a in rheumatoid arthritis (RA) and showed a repressive 
effect of miR-155 on matrix metalloproteinase (MMP) expression in RA synovial 
fibroblasts (RASFs). The present study was undertaken to examine alterations in 
expression of miR-203 in RASFs and analyze its role in fibroblast activation.
METHODS: Differentially expressed miRNA in RASFs versus osteoarthritis synovial 
fibroblasts (OASFs) were identified by real-time polymerase chain reaction 
(PCR)-based screening of 260 individual miRNA. Transfection of miR-203 precursor 
was used to analyze the function of miR-203 in RASFs. Levels of interleukin-6 
(IL-6) and MMPs were measured by real-time PCR and enzyme-linked immunosorbent 
assay. RASFs were stimulated with IL-1β, tumor necrosis factor α (TNFα), 
lipopolysaccharide (LPS), and 5-azacytidine (5-azaC). Activity of IκB kinase 2 
was inhibited with SC-514.
RESULTS: Expression of miR-203 was higher in RASFs than in OASFs or fibroblasts 
from healthy donors. Levels of miR-203 did not change upon stimulation with 
IL-1β, TNFα, or LPS; however, DNA demethylation with 5-azaC increased the 
expression of miR-203. Enforced expression of miR-203 led to significantly 
increased levels of MMP-1 and IL-6. Induction of IL-6 by miR-203 overexpression 
was inhibited by blocking of the NF-κB pathway. Basal expression levels of IL-6 
correlated with basal expression levels of miR-203.
CONCLUSION: The current results demonstrate methylation-dependent regulation of 
miR-203 expression in RASFs. Importantly, they also show that elevated levels of 
miR-203 lead to increased secretion of MMP-1 and IL-6 via the NF-κB pathway and 
thereby contribute to the activated phenotype of synovial fibroblasts in RA.