Down‐regulation of microRNA‐34a* in rheumatoid arthritis synovial fibroblasts promotes apoptosis resistance

Abstract

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 ␣ (TNF␣), interleukin-1␤ (IL-1␤), 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 TNF␣, IL-1␤, 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 miR34a* results in up-regulation of its direct target XIAP, thereby contributing to resistance of RASFs to apoptosis.

Synthetic pre-microRNAs reveal dual-strand activity of miR-34a on TNF-α

“…In one account miR-34c-3p was shown to induce caspase activity in cervical carcinoma cells, though no targets were identified (López and Alvarez-Salas 2011). In another, miR-34a-3p was found to inhibit XIAP, an inhibitor of apoptosis, in synovial fibroblasts (Niederer et al 2011b). Evidence for an extensive activity of miR-34a-3p (as well as miR-34a-5p) was also seen in expression data from cells infected with a miR-34a expression construct (Yang et al 2011).…”

MicroRNAs in rheumatoid arthritis: Altered expression and diagnostic potential

“…TNF-related apoptosis-inducing ligand)-dependent apoptosis in256 RASFs. Thus, the decreased level of miR-34a* contributes to the im-257 paired apoptosis of activated RASFs, the prolonged cellular lifespan of 258 which is important for the pathogenesis of RA[26].…”

Comprehensive Analysis of Serum microRNAs in Autoimmune Pancreatitis

“…The upregulated miRNA, miR-155, was found to repress matrix metalloproteinase 3 [28]. The miR-34* expression was downregulated in rheumatoid arthritis synovial fibroblasts, which led to the inhibition of apoptosis in those cells via X-linked inhibitor of apoptosis protein regulation [29]. These observations indicate the certain involvement of miRNAs in the pathogenesis of immune-related diseases.…”