Accelerating New Bone Formation During Distraction Osteogenesis Using Exosomes And Nanoparticles

BACKGROUND: Distraction osteogenesis is a surgical procedure,which fully induces new bone formation through slow and continuous distraction and possesses unique advantages in treating large bone defects,osteomyelitis,and bone deformity.However,this procedure is limited by the undesirably lengthy consolidation duration with high risk of complications.Therefore,accelerating callus formation and consolidation during distraction osteogenesis and shortening the external fixation time are of great clinical significance.Endothelial progenitor cells(EPCs)are the key participator in angiogenesis while exosomes derived from EPCs(EPC-Exos)also possess the ability to induce new blood vessel formation.Magnetic mesoporous silica nanoparticles(M-MSNs),a promising carrier for drug delivery,may also regulate the differentiation of mesenchymal stem cells(MSCs).At present,the effects of EPC-Exos and M-MSNs on bone regeneration during distraction osteogenesis remain unclear.OBJECTIVE: To evaluate the effects and explore the possible mechanisms of EPC-Exos and M-MSNs on bone regeneration during rat tibial distraction osteogenesis.METHODS: Rat bone marrow derived EPCs were isolated.EPC-Exos were extracted and identified.The effects and mechanisms of EPC-Exos on the proliferation,migration,and tube formation ability of endothelial cells were investigated in vitro.M-MSNs were synthesized and identified.The effects and underlying mechanisms of M-MSNs on the survival,proliferation,and osteogenic differentiation of MSCs were detected.After establishment of rat tibial model of distraction osteogenesis,the effects of EPC-Exos and M-MSNs on angiogenesis and bone regeneration during distraction osteogenesis were examined using X-ray,micro-CT,mechanical,histological,and immunochemical analyses.RESULTS:(1)EPCs were isolated and EPC-Exos were extracted.EPC-Exos were cup-shaped or spherical particles with the diameters ranging from 50 to 150 nm,and expressed exosomal markers.The results of CCK-8,wound healing,and tube formation demonstrated that EPC-Exos significantly enhance the proliferation,migration,and tube formation ability of endothelial cells by activating the Raf/ERK signal pathway,which may be diminished by miR-126 inhibitors.(2)M-MSNs exhibited good biocompatibility and remarkable capability in promoting the osteogenic differentiation of MSCs via activating the Wnt/?-catenin signal pathway in vitro.(3)The results of X-ray imaging,micro-CT,mechanical,histological,and immunochemical analyses demonstrated that both EPC-Exos and M-MSNs dramatically accelerated bone regeneration in the rat tibial model of distraction osteogenesis.CONCLUTIONs:(1)EPC-Exos notably stimulate angiogenesis and promote neo-osteogenesis in a rat model of distraction osteogenesis.(2)EPC-Exos may exert their beneficial effects through transferring miR-126 to the recipient cells,thus activating the Raf/ERK signal pathway.(3)M-MSNs significantly promote the osteogenic differentiation of MSCs in vitro and accelerate new bone formation in the distraction gap.(4)M-MSNs may enhance the osteogenic activity of MSCs and accelerate bone regeneration through activating the Wnt/?-catenin pathway.