OBJECTIVE: To investigate the expression and effect of the microRNA-34 (miR-34) 
family on apoptosis in rheumatoid arthritis synovial fibroblasts (RASFs).
METHODS: Expression of the miR-34 family in synovial fibroblasts with or without 
stimulation with Toll-like receptor (TLR) ligands, tumor necrosis factor α 
(TNFα), interleukin-1β (IL-1β), hypoxia, or 5-azacytidine was analyzed by 
real-time polymerase chain reaction (PCR). Promoter methylation was studied by 
combined bisulfite restriction analysis. The effects of overexpression and 
silencing of miR-34a and miR-34a* on apoptosis were analyzed by annexin 
V/propidium iodide staining. Production of X-linked inhibitor of apoptosis 
protein (XIAP) was assessed by real-time PCR and immunohistochemistry analysis. 
Reporter gene assay was used to study the signaling pathways of miR-34a*.
RESULTS: Basal expression levels of miR-34a* were found to be reduced in 
synovial fibroblasts from RA patients compared to osteoarthritis patients, 
whereas levels of miR-34a, miR-34b/b*, and miR-34c/c* did not differ. Neither 
TNFα, IL-1β, TLR ligands, nor hypoxia altered miR-34a* expression. However, we 
demonstrated that the promoter of miR-34a/34a* was methylated and showed that 
transcription of the miR-34a duplex was induced upon treatment with 
demethylating agents. Enforced expression of miR-34a* led to an increased rate 
of FasL- and TRAIL-mediated apoptosis in RASFs. Moreover, levels of miR-34a* 
were highly correlated with expression of XIAP, which was found to be 
up-regulated in RA synovial cells. Finally, we identified XIAP as a direct 
target of miR-34a*.
CONCLUSION: Our data provide evidence of a methylation-specific down-regulation 
of proapoptotic miR-34a* in RASFs. Decreased expression of miR- 34a* results in 
up-regulation of its direct target XIAP, thereby contributing to resistance of 
RASFs to apoptosis.