Osteoblast-derived exosome mediating the effect of microRNA-494 on bone metabolism and bone remodeling balance in osteoporotic rats
Objective To investigate the effect of osteoblast-derived exosome(Exo)mediating microRNA(miR)-494 on bone metabolism and bone remodeling balance in osteoporosis(OP)rats and its mechanism.Methods Exosomes was isolated and identified from MC3T3-E1 osteoblast cell line and transferred to Exo by electrical transfer.Forty SD rats were randomly divided into control,model,miR-494 mimic(miR-494),and miR-494 inhibitor group,10 rats in each group.The ovaries were removed to construct the OP model except the control group.After modeling,the miR-494 group and miR-494 inhibitor group received tail vein injections of exosomes containing the corresponding miRNA,at a dose of 3×109 particles.Four weeks later,bone parameters were detected in each group of rats by Micro-CT,serum bone markers were measured by ELISA,pathological changes in bone tissue were observed by HE staining,osteoclast numbers were detected by tartrate-resistant acid phosphatase(TRACP)staining,and the expression levels of bone remodeling-related proteins and toll-like receptor 4(TLR4)pathway-related proteins were determined by Western blotting.Results Typical cup-shaped or round exosomes were successfully isolated with a diameter of about 100 nm from MC3T3-E1 cells,which contained CD63,CD9,tumor susceptibility gene 101(TSG101),heat shock protein 70(HSP70)proteins and can be taken up by MC3T3-E1 cells.Compared with the model group,the bone parameters of the rats in the miR-494 mimic group decreased,serum bone markers bone Gla protein(BGP),TRACP,C-terminal telopeptide of type Ⅰ collagen(CTX-Ⅰ)increased,osteoprotegerin(OPG),procollagen type Ⅰ N-terminal propeptide(PⅠNP)decreased,bone trabeculae structure was disordered,osteoclasts increased,bone morphogenetic protein 2(BMP-2),Runt related transcription factor 2(RUNX2)in bone tissue downregulated,receptor activator of nuclear factor kappa-B ligand(RANKL)upregulated,TLR4,nuclear factor kappa-B p65(NF-κB p65)and myeloid differentiation primary response 88(MyD88)upregulated(all P＜0.05).In contrast,the situation of the miR-494 inhibitor group was opposite,bone parameters and OPG,PⅠNP increased,BGP,TRACP,CTX-Ⅰdecreased,bone structure returned to normal,osteoclasts decreased,BMP-2,RUNX2 in bone tissue upregulated,RANKL downregulated,TLR4,NF-κB p65 and MyD88 downregulated(all P＜0.05).Conclusion The transfer of miRNA-494 by Exo aggravates abnormal bone metabolism in OP rats and inhibits bone remodeling balance,suggesting that the mechanism of action may be related to the regulation of TLR4 pathway.
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