Osteoclast-derived miR-23a-5p-containing exosomes inhibit osteogenic differentiation by regulating Runx2

Some microRNAs (miRNAs) are involved in osteogenic differentiation. In recent years, increasing evidences have revealed that exosomes contain specific miRNAs. However, the effect and mechanism of miR-23a-5p-containing exosomes in osteoblast remain largely unclear.

We extracted exosomes from RANKL-induced RAW 264.7 cells, and identified exosomes via transmission electron microscopy, western blot and flow cytometry analysis. In addition, exosome secretion was inhibited by GW4869 and Rab27a siRNAs. miR-23a-5p expression was analyzed by qRT-PCR, and the related protein levels were examined by western blot assay. Furthermore, the number and distribution of osteoclasts were detected by TRAP staining, and early osteogenesis was evaluated by ALP staining. Combination of YAP1 and Runx2 was verified by Co-IP assay, and the regulation of miR-23a-5p and Runx2 was measured by dual luciferase reporter assay.

We successfully extracted exosomes from RANKL-induced RAW 264.7 cells, and successfully verified exosomes morphology. We also indicated that miR-23a-5p was highly expressed in exosomes from RANKL-induced RAW 264.7 cells, and osteoclast-derived miR-23a-5p-containing exosomes inhibited osteoblast activity, while its inhibition weakened osteoclasts. In mechanism, we demonstrated that Runx2 was a target gene of miR-23a-5p, YAP interacted with Runx2, and YAP or Runx2 inhibited MT1DP expression. In addition, we proved that knockdown of MT1DP facilitated osteogenic differentiation by regulating FoxA1 and Runx2.

We demonstrated that osteoclast-derived miR-23a-5p-containing exosomes could efficiently suppress osteogenic differentiation by inhibiting Runx2 and promoting YAP1-mediated MT1DP. Therefore, we suggested miR-23a-5p in exosomes might provide a novel mechanism for osteoblast function.