miR-765 inhibits the osteogenic differentiation of human bone marrow mesenchymal stem cells by targeting BMP6 via regulating the BMP6/Smad1/5/9 signaling pathway

BACKGROUND: The process of bone repair is heavily dependent on the ability of human bone marrow mesenchymal stem cells (hMSCs) to undergo osteogenic differentiation. MicroRNAs have been shown to regulate this osteogenic process. This study aimed to investigate the role of miR-765 in the osteogenic differentiation of hMSCs. METHODS: We transfected hMSCs with lentiviral constructs to knock down or overexpress this miRNA, allowing us to assess its role in osteogenesis via assessing the expression of the relevant markers alkaline phosphatase (ALP), runt-related gene-2 (RUNX-2), and osteocalcin (OCN), with further functional measurements made via quantifying ALP activity and conducting Alizarin Red S staining. The targeting of the 3′-untranslated region (UTR) of BMP6 by miR-765 was examined via luciferase assay. We used hMSCs with altered miR-765 expression to assess p-Smad1/5/9 levels via Western blotting over the course of osteogenic differentiation. We also assessed the osteogenic differentiation of hMSCs in which miR-765 was knocked down and at the same time as a BMP/Smad signaling inhibitor was added to disrupt Smad1/5/9 phosphorylation. RESULTS: We found miR-765 overexpression to inhibit osteogenesis-associated gene upregulation during osteogenic differentiation of hMSCs, whereas knockdown of this miRNA was associated with increased expression of these genes. Using luciferase reporter assays, we confirmed direct miR-765 binding to the 3′-untranslated region (UTR) of BMP6. We also found that miR-765 overexpression reduced Smad1/5/9 phosphorylation, and knockdown of this miRNA enhanced this phosphorylation on BMP6/Smad1/5/9 signaling. The osteogenic differentiation of hMSCs in which miR-765 had been knocked down was further weakened upon the addition of a BMP/Smad signaling inhibitor relative to miR-765 knockdown alone. CONCLUSIONS: Together, these results thus suggest that miR-765 is able to inhibit hMSC osteogenic differentiation by targeting BMP6 via regulation of the BMP6/Smad1/5/9 signaling pathway. Our findings may offer molecular insights of value for the development of novel therapeutic treatments for bone diseases including osteoporosis.