miR-21 promotes osteoclastogenesis through activation of PI3K/Akt signaling by targeting Pten in RAW264.7 cells

The present study aimed to investigate the effects of microRNA (miR)-21 on osteoclastogenesis and its underlying molecular mechanisms. The expression levels of tartrate-resistant acid phosphatase (TRAP) and miR-21 were detected during osteoclastogenesis in receptor activator of NF-κB ligand (RANKL)-induced RAW264.7 cells via reverse transcription-quantitative PCR. Bioinformatics and dual luciferase reporter assays were performed to analyze the association between miR-21 and Pten. RANKL-induced RAW264.7 cells were divided into the following groups: MiR-negative control (NC), miR-21 mimic, miR-21 inhibitor and miR-21 mimic + LY294002. The effects of miR-21 on osteoclastogenesis and bone resorption were then detected using TRAP staining and a bone resorption assay. Pten, phosphorylated-Akt and nuclear factor of activated T cell (NFATc1) expression levels were measured by western blotting to analyze the effects of miR-21 on the PI3K/Akt signaling pathway. The present study revealed that miR-21 was upregulated during osteoclastogenesis in RANKL-induced RAW264.7 cells. Furthermore, miR-21 negatively regulated Pten. Compared with the miR-negative control (NC) group, the number of osteoclasts and the percentage of bone resorption were increased in the miR-21 mimic group, whereas they were decreased in the miR-21 inhibitor group. The number of osteoclasts and the percentage of bone resorption in the miR-21 mimic + LY294002 group were lower than in the miR-21 mimic group. Compared with the miR-NC group, the protein expression levels of Pten were decreased, whereas p-Akt and NFATc1 were increased in the miR-21 mimic group. Conversely, Pten protein expression was increased, whereas p-Akt and NFATc1 were decreased in the miR-21 inhibitor group. In the miR-21 mimic + LY294002 group, Pten protein expression was higher, and p-Akt and NFATc1 were lower than in the miR-21 mimic group. In conclusion, miR-21 is upregulated during osteoclastogenesis, and may promote osteoclastogenesis and bone resorption through activating the PI3K/Akt signaling pathway via targeting Pten.