Background and Objective: Tumor necrosis factor alpha (TNF-α), a cytokine involved in the pathogenesis of periodontal disease, induces osteoclast differentiation and indirectly promotes alveolar bone resorption. We investigated TNF-α-regulated osteoclast differentiation, focusing on microRNAs. MicroRNAs are small, noncoding RNAs that are involved in various biological processes, including cellular differentiation, proliferation and apoptosis. Aside from miR-21, miR-155 and miR-223, the identities of the microRNAs that play roles in osteoclast differentiation are unknown. Notably, no previous studies have reported the expression profiling of microRNAs during TNF-α-regulated osteoclast differentiation. Material and Methods: We used microarrays to screen the levels of expression of mature microRNAs in RAW264.7 cells treated with a combination of TNF-α and RANKL, or RANKL alone for 0, 24 or 82 h during osteoclast formation. We validated the results of the microarray analyses through quantitative RT-PCR analyses of representative microRNAs in RAW264.7 cells and murine bone marrow macrophages. Results: During osteoclast formation, the expression of 44 mature microRNAs differed by more than twofold between untreated cells and cells treated with a combination of TNF-α and RANKL, and the expression of 52 mature microRNAs differed upon RANKL treatment. According to quantitative RT-PCR analyses, miR-378 was upregulated and miR-223 was downregulated during osteoclast formation. Furthermore, miR-21, miR-29b, miR-146a, miR-155 and miR-210 were highly expressed during osteoclast differentiation in TNF-α/RANKL-treated cells compared with RANKL-treated cells. Conclusions: These results suggest that miR-223 and miR-378 may play important roles in osteoclastogenesis, and that miR-21, miR-29b, miR-146a, miR-155 and miR-210 are involved in TNF-α-regulated osteoclast differentiation.
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