DNA Methylation Variability in a Single Locus of the RXRα Promoter from Umbilical Vein Blood at Term Pregnancy

DNA methylation status of RXR alpha gene promoter has been correlated with maternal diet during early pregnancy, and associated with offspring's adiposity and bone mineral content. In adult life, increased methylation of RXR alpha promoter region is associated with myocardium pathologies. Early growth response proteins (EGR) are zinc finger transcription factors associated with several cellular pathways such as inflammation, apoptosis, and cardiopathies. DNA-binding sequences of EGR proteins have been reported in the RXR alpha gene promoter using chromatin immunoprecipitation methods. Here, we used correlations between the maternal pre-pregnancy body mass index (p-BMI), gestational weight gain (GWG), and birth weight (BW) as indirect indicators of the maternal nutritional status as modifier of DNA methylation in the offspring. DNA methylation status from newborns' umbilical vein blood in full-term pregnancy was evaluated in a short sequence (116 pb) of the RXR alpha gene promoter that contains the elements of response sequence for EGR proteins. Fifty-three bisulfite-modified DNA samples were assessed through methyl-sensitive high-resolution melting (MS-HRM) analysis. To validate the results, we directly sequenced MS-HRM samples to confirm the presence of CpG-methylated positions. In addition, the RXR alpha protein levels in extracts of umbilical vein blood were evaluated by western blot. We found differential methylation in a specific locus of the RXR alpha promoter surrounding the EGR-binding sequence; however, no correlation was found with the level of RXR alpha protein expression. Variability in the methylation status of the RXR alpha promoter near the EGR transcription factor binding site in newborn cord blood provides controversial epigenetic insights into RXR alpha regulation via EGR proteins.