With the increasing application of microRNAs (miRNAs) in the treatment and monitoring of different diseases, miRNAs have become an important tool in biological and medical research. Recent studies have proven that miRNAs are involved in the osteogenic differentiation of stem cells. However, few studies have reported the use of miRNA-modified adult stem cells to repair critical-sized defects (CSDs) using tissue engineering technology. It is known that miR-31 is a pleiotropically acting miRNA that inhibits cancer metastasis and targets special AT-rich sequence-binding protein 2 (Satb2) in fibroblasts. However, it is not clear whether the function of miR-31 is to enhance adipose tissue-derived stem cell (ASC) osteogenesis, along with its association with Satb2, during osteogenic differentiation and bone regeneration. In this study, we systematically evaluated the function of miR-31 in enhancing ASC osteogenesis and the therapeutic potential of miR-31-modified ASCs in a rat CSD model with β-tricalcium phosphate (β-TCP) scaffolds. ASCs were treated with lentivirus (Lenti)-miR-31, Lenti-as-miR-31 (antisense) or Lenti-NC (negative control). These genetically modified ASCs were then combined with β-TCP scaffolds to repair CSDs in rats. The results showed that in cultured ASCs in vitro, Lenti-as-miR-31 significantly enhanced osteogenic mRNA and protein expression when compared with the Lenti-NC group. Moreover, we firstly found that a Runt-related transcription factor 2 (Runx2), Satb2 and miR-31 regulatory loop triggered by bone morphogenetic protein-2 (BMP-2) plays an important role in ASCs' osteogenic differentiation and bone regeneration. More importantly, we found that miR-31-knockdown ASCs dramatically improved the repair of CSDs, including increased bone volume, increased bone mineral density (BMD) and decreased scaffold residue in vivo. These data confirm the essential role of miR-31-modified ASCs in osteogenesis in vitro and in vivo.
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