MiR-27a is Essential for the Shift from Osteogenic Differentiation to Adipogenic Differentiation of Mesenchymal Stem Cells in Postmenopausal Osteoporosis.

BACKGROUND/AIMS: Osteoporosis is a progressive bone disease characterized by a decrease in bone mass and density, which results in an increased risk of fractures. Mesenchymal stem cells (MSCs) are progenitor cells that can differentiate into osteoblasts, osteocytes and adipocytes in bone and fat formation. A reduction in the differentiation of MSCs into osteoblasts contributes to the impaired bone formation observed in osteoporosis. MicroRNAs (miRNAs) play a regulatory role in osteogenesis and MSC differentiation. MiR-27a has been reported to be down-regulated in the development of osteoporosis and during adipogenic differentiation.

METHODS: In this study, a miRNA microarray analysis was used to investigate expression profiles of miRNA in the serum of osteoporotic patients and healthy controls and this data was validated by quantitative real-time PCR (qRT-PCR). MSCs isolated from human and mice with miR-27a inhibition or overexpression were induced to differentiate into osteoblasts or adipocytes. TargetScan and PicTar were used to predict the target gene of miR-27a. The mRNA or protein levels of several specific proteins in MSCs were detected using qRT-PCR or western blot analysis. Ovariectomized mice were used as in vivo model of human postmenopausal osteoporosis for bone mineral density measurement, micro-CT analysis and histomorphometric analysis.

RESULTS: Here, we analyzed the role of miR-27a in bone metabolism. Microarray analysis indicated that miR-27a expression was significantly reduced in osteoporotic patients. Analysis on MSCs derived from patients with osteoporosis indicated that osteoblastogenesis was reduced, whereas adipogenesis was increased. MSCs that had undergone osteoblast induction showed a significant increase in miR-27a expression, whereas cells that had undergone adipocyte induction showed a significant decrease in miR-27a expression, indicating that miR-27a was essential for MSC differentiation. We demonstrated that myocyte enhancer factor 2 c (Mef2c), a transcription factor, was the direct target of miR-27a using a dual luciferase assay. An inverse relationship between miR-27a expression and Mef2c expression in osteoporotic patients was shown. Silencing of miR-27a decreased bone formation, confirming the role of miR-27a in bone formation in vivo.

CONCLUSION: In summary, miR-27a was essential for the shift of MSCs from osteogenic differentiation to adipogenic differentiation in osteoporosis by targeting Mef2c.