Posttranscriptional Interaction Between miR-450a-5p and miR-28-5p and STAT1 mRNA Triggers Osteoblastic Differentiation of Human Mesenchymal Stem Cells.

We demonstrate that the interaction between miR-450a-5p and miR-28-5p and signal transducer and activator of transcription 1 (STAT1) mRNA correlates with the osteoblastic differentiation of mesenchymal stem cells from human exfoliated deciduous teeth (shed cells). STAT1 negatively regulates runx-related transcription factor 2 (RUNX2), which is an essential transcription factor in this process. However, the elements that trigger osteoblastic differentiation and therefore pause the inhibitory effect of STAT1 need investigation. Usually, STAT1 can be posttranscriptionally regulated by miRNAs. To test this, we used an in vitro model system in which shed cells were chemically induced toward osteoblastic differentiation and temporally analyzed, comparing undifferentiated cells with their counterparts in the early (2 days) or late (7 or 21 days) periods of induction. The definition of the entire functional genome expression signature demonstrated that the transcriptional activity of a large set of mRNAs and miRNAs changes during this process. Interestingly, STAT1 and RUNX2 mRNAs feature contrasting expression levels during the course of differentiation. While undifferentiated or early differentiating cells express high levels of STAT1 mRNA, which was gradually downregulated, RUNX2 mRNA was upregulated toward differentiation. The reconstruction of miRNA-mRNA interaction networks allowed the identification of six miRNAs (miR-17-3p, miR-28-5p, miR-29b, miR-29c-5p, miR-145-3p, and miR-450a-5p), and we predicted their respective targets, from which we focused on miR-450a-5p and miR-28-5p STAT1 mRNA interactions, whose intracellular occurrence was validated through the luciferase assay. Transfections of undifferentiated shed cells with miR-450a-5p or miR-28-5p mimics or with miR-450a-5p or miR-28-5p antagonists demonstrated that these miRNAs might play a role as posttranscriptional controllers of STAT1 mRNA during osteoblastic differentiation. J. Cell. Biochem. 118: 4045-4062, 2017. © 2017 Wiley Periodicals, Inc.