Abstract
Several miRNAs have recently been identified to regulate adipocyte or osteoblast differentiation or both. In this study, miR-223 was found to be involved in the reciprocal regulation of adipocyte and osteoblast differentiation. miR-223 was induced in primary cultured mouse marrow stromal cell, mesenchymal line C3H10T1/2 and stromal line ST2 after adipogenic treatment. Conversely, it was reduced in preosteoblast MC3T3-E1 after osteogenic treatment. Supplementing miR-223 levels using synthetic miR-223 mimics significantly suppressed the growth of the C3H10T1/2 and ST2 cells and induced the progenitor cells to fully differentiate into adipocytes, along with induction of adipocyte-specific transcription factors peroxisome proliferator-activated receptor γ, CCAAT/enhancer binding protein-α (C/EBPα), and marker genes aP2 and adipsin. By contrast, depletion of the endogenous miR-223 using synthetic miR-223 inhibitor repressed the progenitor cells to differentiate. The effects of miR-223 on adipocyte formation from ST2 cells were also demonstrated by using lentivirus that overexpresses miR-223. Conversely, supplementing miR-223 blocked ST2 to differentiate into osteoblasts. Fibroblast growth factor receptor 2 (Fgfr2), a critical regulator of osteoblast, was shown to be a direct target of miR-223 by using dual luciferase reporter assay. Knockdown of Fgfr2 in C3H10T1/2 downregulated phosphorylation of ERK1/2 and upregulated expression of C/EBPα and dramatically enhanced the differentiation of the cells into adipocytes. Further investigation of mechanisms that control miR-223 expression demonstrated that C/EBPs induced miR-223 expression through binding to the promoter regions of the miR-223. Taken together, our study provides evidences that miR-223 regulates adipocyte and osteoblast differentiation through a novel C/EBPs/miR-223/FGFR2 regulatory feedback loop.