MicroRNAs are short (~25 nucleotides) RNAs that play a major role in the regulation of gene expression in many eukaryotic cellular processes. Many microRNAs have been reported to be involved in bone formation and remodelling. We have generated and characterised a new mouse strain (Dicerosx) that can be utilised to study the role of osteoblast specific microRNAs in skeletal maturation and fracture healing. It was generated by crossing Dicer flox/flox mice with OsxCreERT2 mice. Animal studies were approved by the Finnish Animal Ethics Committee. In this strain, by administering tamoxifen to Cre positive(OsxCreERT2-dicer floxed) mice, dicer can be inactivated in osterix expressing osteoblasts. Tamoxifen was given to young (3 weeks) and old (10 weeks) Cre positive and corresponding control mice for 3 days and they were followed for 5 weeks. The animals were then sacrificed and femura were analysed by MicroCT analysis. We found a significant reduction in the cortical bone volume and thickness in the Cre+ male and female mice, accompanied by reduced bone perimeter in the male mice, but not in female mice. We also studied the effects of Dicer inactivation in Osterix expressing osteoblasts during fracture healing. Under anaesthesia, closed tibial fractures were generated in Cre positive male mice as well as in Cre negative controls. Prior to the fracture, a small steel rod was inserted in the tibial shaft using surgical procedures. The animals were sacrificed at d14 and the calluses were analysed by MicroCT analysis. As compared with the controls, the total callus volume was decreased in the Cre positive animals. However, there was no significant difference in the amount of mineral deposited within the calluses. MicroRNAs appear to be important in the regulation of periosteal osteoblastic cells which was manifested as reduced cortical bone volume in the dicer inactivated animals.
Disclosure: The authors declared no competing interests. This work was funded by the Academy of Finland (Grant Decision number - 250917).