MicroRNA-155 (miR-155) inhibits BMP9-induced osteogenesis and stimulates TNF-α-mediated osteoclastogenesis. However, the role of miR-155 on bone regeneration and bone mass has not been investigated yet. This study aimed to examine the role of miR-155 on osteogenic differentiation of mMSCs in vitro, and bone regeneration and bone mass in vivo. miR-155 -/- mice were obtained from The Jackson laboratory. While miR-155 KI mice were constructed by the CRISPR method. We analyzed femoral bone mass in miR-155 -/- , and miR-155 KI mice (7 weeks, n=4) by micro-CT. miR-155 was silenced with sponged-lentivirus in mouse BMSCs (mBMSCs), then cell migration and osteogenic differentiation were analyzed in vitro. BMP-2 (2 μg) loaded collagen film was ectopically transplanted in miR-155 transgenic mice and ectopic bone regeneration was evaluated by micro-CT. Ethical approval was obtained for animal study. The selected significance level was Pb 0.05. Micro-CT data and quantification of bone parameters (BMD, BV/TV, Tb. N, Tb. Th, and Tb. Sp) showed that the bone mass was decreased in miR-155 KI mice and increased in miR-155 -/- male mice. In miR-155 KI mice BMD, BV/TV, Tb.N, and Tb. Th were reduced by 0.8-, 0.7-, 0.8-, and 0.9-fold, respectively, compared to wildtype mice. In miR-155 -/- mice, BMD, BV/TV, and Tb.N were increased 1.7-, 1.6-, and 1.6-fold, respectively, compared to wildtype mice. Matrix mineralization (Alizarin red staining, ARS) was enhanced in miR-155 knockdown mBMSCs culture. mBMSCs migration was significantly increased in the miR- 155 knockdown group. Micro-CT images and quantification showed that the ectopic bone formation was reduced in miR-155 KI mice and enhanced in miR-155 -/- mice. In conclusion, miR-155 showed an inhibitory effect on migration and osteogenic differentiation of mMSCs, bone regeneration, and bone mass. Therefore, miR-155 could be the possible therapeutic target to improve stem cell-based bone defect healing and to treat the diseases with low bone mass phenotype.
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