DNA methylation and gene expression of sFRP2, sFRP4, Dkk 1, and Wif1 during osteoblastic differentiation of bone marrow derived mesenchymal stem cells.

OBJECTIVES:Bone marrow derived mesenchymal stem cells (BMSCs) are an irresistible choice for use in stem cell therapy and regenerative medicine. BMSCs osteoblastic differentiation is also important in bone development, diseases, malignancies, and cancers studies. Wnt signaling pathway antagonists, Dickkopf-1 (Dkk 1), Secreted Frizzled-Related Proteins (sFRPs), and Wnt Inhibitory Factor 1 (Wif1) play important roles in inducing osteoblastic differentiation. This study is the first to investigate the association between DNA methylation and gene expression of Dkk1, sFRP2, sFRP4, and Wif1 during BMSCs osteoblastic differentiation. METHODS:Human BMSCs were isolated and characterized using flow cytometry. Then, cells were treated with osteo-differentiation medium for three weeks. Alizarin red S staining and polymerase chain reaction (PCR) (alkaline phosphatase/osteocalcin) were performed for confirmation. The expression of Dkk 1, sFRP2, sFRP4, and Wif1 genes was evaluated at days 7, 14, and 21 using real-time PCR. Methylation-specific PCR (MSP) was performed to detect the methylation status of the promoters of the genes. RESULTS:Data showed significant decreases (P < 0.05) during various days of BMSCs differentiation, while the promoters of the genes remained mostly un-methylated. CONCLUSIONS:The down-regulation of Dkk 1, sFRP2, sFRP4, and Wif1 regulates various stages of human BMSCs during osteoblastic differentiation. DNA methylation does not interfere in the down-regulation of these genes, except for Wif1. We propose that the Wnt antagonist gene promoters should remain un-methylated during osteoblastic differentiation of BMSCs and that the down-regulation of these genes may contribute to other epigenetic mechanisms, other than DNA methylation, which implicitly indicates the role of DNA methylation in osteogenic cancers.

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