Influence of DNA methylation on the expression of OPG/RANKL in primary osteoporosis

Purpose: A key factor in regulating bone absorption is the proportion of RANKL/OPG. Although many reports showing diverse transcription factors or epigenetic modification could be responsible for regulating RANKL&OPG ratio, there is still little exploration on promoter methylation status of both genes in osteoporotic bone tissues. Our aim is to investigate the changes of methylation in CpG island of these genes' promoters in patients with primary osteoporosis. Methods: The diagnosis of osteoporosis was based on the results of dual energy X-ray absorptiometry measurements. All femoral bone tissues were separated in surgeries. After extracting total RNA, we checked the relative expression levels of OPG and RANKL by quantitative real time PCR. The genomic DNA of Non-OPF (Non-osteoporotic fracture bone tissues) & OPF (osteoporotic fracture bone tissues) were treated by bisulfite modification, and methylation status of CpG sites in the CpG island of OPG/RANKL promoters were determined by DNA sequencing. Results: RANKL expression in the OPF group was significantly higher than that in Non-OPF group, and the CpG methylation status in RANKL gene promoter was significantly lower. However, for OPG, lower gene expression level and higher methylation degree were found in the OPF group. Conclusion: Our study demonstrated that DNA methylation influenced the transcriptional expression of OPG and RANKL, which probably take on a "main switch" role in pathogenesis of primary osteoporosis.