OBJECTIVE: Several microRNA, which are approximately 22-nucleotide noncoding 
RNAs, exhibit tissue-specific or developmental stage-specific expression 
patterns and are associated with human diseases. The objective of this study was 
to identify the expression pattern of microRNA-146 (miR-146) in synovial tissue 
from patients with rheumatoid arthritis (RA).
METHODS: The expression of miR-146 in synovial tissue from 5 patients with RA, 5 
patients with osteoarthritis (OA), and 1 normal subject was analyzed by 
quantitative reverse transcription-polymerase chain reaction (RT-PCR) and by in 
situ hybridization and immunohistochemistry of tissue sections. Induction of 
miR-146 following stimulation with tumor necrosis factor alpha (TNFalpha) and 
interleukin-1beta (IL-1beta) of cultures of human rheumatoid arthritis synovial 
fibroblasts (RASFs) was examined by quantitative PCR and RT-PCR.
RESULTS: Mature miR-146a and primary miR-146a/b were highly expressed in RA 
synovial tissue, which also expressed TNFalpha, but the 2 microRNA were less 
highly expressed in OA and normal synovial tissue. In situ hybridization showed 
primary miR-146a expression in cells of the superficial and sublining layers in 
synovial tissue from RA patients. Cells positive for miR-146a were primarily 
CD68+ macrophages, but included several CD3+ T cell subsets and CD79a+ B cells. 
Expression of miR-146a/b was markedly up-regulated in RASFs after stimulation 
with TNFalpha and IL-1beta.
CONCLUSION: This study shows that miR-146 is expressed in RA synovial tissue and 
that its expression is induced by stimulation with TNFalpha and IL-1beta. 
Further studies are required to elucidate the function of miR-146 in these 
tissues.