| Research background and purpose:MicroRNAs(miRNAs)are a type of non-coding single-stranded RNAs composed of 18-24 amino acid molecules.They play a regulatory role by combining with specific sequences of target genes post-transcriptionally.With the deepening research,people have found that miRNAs exist in almost all eukaryotic cells and some viruses and regulate more than 30%of protein-coding genes.They play an extensively regulatory role in cell proliferation,differentiation,apoptosis and the growth and development of tissues and organs.miR-21 is an important member of the miRNAs family and one of the earliest miRNAs found in mammals,expressed in tissues and cells of many species.Now a large number of studies have found that miR-21 is closely related to the occurrence and development of a variety of diseases.miR-21 expression increased in colorectal cancer,cervical cancer,gastric cancer,breast cancer and other cancers and tumors.Studies also found that miR-21 can promote fibrosis of fibroblasts,leading to or aggravating the occurrence of cardiovascular disease;miR-21 also plays certain role in promoting differentiation of osteoblasts and osteoclasts in osteoporosis patients.Bone defect is one of the most common clinical diseases.Its treatment is difficult and has a long course,which greatly impact the patients both physically and psychologically.miR-21 has been proved to promote osteogenic differentiation of various types of stem cells,but relative vivo studies are rare.The research on the mechanism of miR-21 in the process of bone regeneration is of great theoretical significance for enriching people's cognition of miR-21,and has certain practical value in guiding clinical diagnosis and treatment of bone defects.This study aims to establish the model of maxillary bone defect in mice,and to explore the effect of miR-21 on bone regeneration by comparing the healing ability of miR-21 in both knock-out mice and wild-type mice.Research methods:1.Select eight-week-old female C57BL/6 wild-type mice and miR-21 knock-out mice to establish the model of maxillary bone defect.The natural healing was observed.After 8 weeks and 12 weeks,the effects of miR-21 on bone regeneration were observed by gross observation on the sample,micro-CT examination,HE staining,Masson trichrome staining and immunohistochemically staining.2.To further verify the regulatory role of miR-21 in bone regeneration,we established a rescue model of miR-21 knock-out mice.MiR-21 overexpression agents(miR-21 agomir)were injected intraperitoneally into the miR-21 knock-out mice and were sacrificed 8 weeks later.The specimens were examined by micro-CT,HE staining and Masson trichrome staining,immunohistochemically staining and other methods to observe the bone healing.Result:1.The results of micro-CT scan showed that in the same time period,wild-type mice had larger bone healing area and new bone mass than miR-21 knock-out mice,and the thickness of trabecular bone in newborn bone were higher.The results of HE staining showed that the newborn bone mass of wild-type mice was significantly more than that of the wild-type mice in the same time period.Masson trichrome staining showed that in the same time period,wild-type mice had more new bone mass and higher bone maturity.Immunohistochemically staining showed that the expression levels of osteogenic factors ALP and OCN were also higher in wild type mice.2.The mice injected with miR-21 overexpressing agent intraperitoneally were sacrificed 8 weeks after the operation.The results of micro-CT scan showed that the amount of new bone in the bone defect of the rescue group was significantly more than that of the miR-21 knock-out group,and new bone trabecular thicker.The result of HE staining showed that there were more new bone in the bone defect in the rescue group.The Masson trichrome staining showed that the new bone mass in the rescue group was higher and the newborn bone maturity is also higher.Immunohistochemically staining showed that the expression levels of osteogenic factors ALP and OCN in miR-21-KO+agomir group were higher than those in miR-21-KO group.Moreover,Micro-CT showed that the new bone volume of miR-21-KO+agomir group was higher than that of WT mice,and the density and thickness of trabecular were higher.Conclusion:1.The results of micro-CT scan and tissue section staining showed that the WT group had a stronger bone healing ability than the miR-21-KO group.Therefore,we can speculate that the miR-21 gene affects the process of maxillary bone healing,and the knockout of the miR-21 gene inhibits the healing of maxillary bone defects.2.The results of micro-CT scan and tissue section staining showed that the bone healing ability of miR-21-KO+agomir mice was stronger than that of miR-21-KO group.miR-21 over expression reagents could improve the maxillary bone healing ability of miR-21-KO mice and accelerate the formation and mineralization of the new bone.The miR-21 gene positively regulates the process of maxillary bone healing. |
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