Methylation of the Sclerostin Gene in Serum Free DNA: A New Bone Biomarker?

Cell-free DNA (cfDNA) methylation is an important molecular biomarker, which provides information about the regulation of gene expression in the tissue of origin. There is an inverse correlation between gene methylation and expression levels. We analyzed promoter methylation in cfDNA from serum, and compared it with DNA from blood and bone cells from patients undergoing hip replacement surgery. We also measured cfDNA methylation in 28 osteoporotic patients at baseline and after 6 months of antiosteoporotic therapy (alendronate, teriparatide, or denosumab). gene promoter methylation levels in serum cfDNA were very similar to those of bone-derived DNA (79% ± 12% and 82% ± 7%, respectively), but lower than methylation levels in blood cell DNA (87% ± 10%). Furthermore, there was a positive correlation between an individual's DNA methylation values in serum and bone. No differences in either serum sclerostin levels or methylation were found after 6-months of therapy with antiosteoporotic drugs. Our results suggest that serum cfDNA does not originate from blood cells, but rather from bone. However, since we did not confirm changes in this marker after therapy with bone-active drugs, further studies examining the correlation between bone changes of expression and methylation in cfDNA are needed to confirm its potential role as a bone biomarker.