MicroRNA-205 mediates endothelial progenitor functions in distraction osteogenesis by targeting the transcription regulator NOTCH2.

BACKGROUND: Distraction osteogenesis (DO) is a highly efficacious form of reconstructive bone regeneration, but its clinical utility is limited by the prolonged period required for bone consolidation to occur. Understanding the mechanistic basis for DO and shortening this consolidation phase thus represent promising approaches to improving the clinical utility of this procedure.
METHODS: A mandibular DO (MDO) canine model was established, after which small RNA sequencing was performed to identify relevant molecular targets genes. Putative miRNA target genes were identified through bioinformatics and confirmed through qPCR, Western blotting, and dual-luciferase reporter assays. Peripheral blood samples were collected to isolate serum and endothelial colony-forming cells (ECFCs) in order to measure miR-205, NOTCH2, and angiogenic cytokines expression levels. Lentiviral constructs were then used to inhibit or overexpress miR-205 and NOTCH2 in isolated ECFCs, after which the angiogenic activity of these cells was evaluated in migration, wound healing, proliferation, tube formation, and chick chorioallantoic membrane (CAM) assay. Autologous ECFCs transfected to knockdown miR-205 and were injected directly into the distraction callus. On days 14, 28, 35 and 42 after surgery, bone density was evaluated via CBCT, and callus samples were collected and evaluated via histological staining to analyze bone regeneration and remodeling.
RESULTS: MiR-205 was identified as being one of the miRNAs that was most significantly downregulated in MDO callus samples. Downregulation of miR-205 was also observed in DO-ECFCs and serum of animals undergoing MDO. Inhibiting miR-205 markedly enhanced angiogenesis, whereas overexpressing miR-205 had the opposite effect in vitro. Importantly, NOTCH2, which is a unique regulator in bone angiogenesis, was identified as a miR-205 target gene. Consistent with this regulatory relationship, knocking down NOTCH2 suppressed angiogenesis, and transduction with a miR-205 inhibitor lentivirus was sufficient to rescue angiogenic activity. When ECFCs in which miR-205 had been inhibited were transplanted into the MDO callus, this significantly bolstered osteogenesis, and remodeling in vivo.
CONCLUSIONS: MiR-205 is a significant regulator of the MDO process, and inhibiting this miRNA can accelerate MDO-related mineralization. Overall, these results offer new insights into the mechanistic basis for this procedure, highlighting potential targets for therapeutic clinical intervention.