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Background  DNA methylation at specific CpG sites within gene promoter regions is known to regulate transcriptional activity  in vitro . In human adipose tissue, basal transcription of the aromatase (CYP19A1) gene is driven primarily by the I.4 promoter however the role of DNA methylation in regulating expression in  ex vivo  mature adipocytes is unknown. This observational study reports the correlation of DNA methylation within the I.4 promoter region of human mature subcutaneous and omental adipocytes with aromatase expression and body composition measures.    Methods  Omental and subcutaneous adipose tissue were collected from 25 obese subjects undergoing bariatric surgery and the mature adipocyte fraction purified. DNA methylation status of 5 CpG sites within a 550 base pair region encompassing the transcription start site (TSS) of promoter I.4 was determined using pyrosequencing. Relative aromatase and I.4 promoter specific mRNA expression was determined by qRT-PCR and whole body DXA performed in 25 participants.    Results  Site-specific DNA methylation varied from 21 ± 10% to 81 ± 11%. In omental adipocytes percentage methylation at the I.4.1 and I.4.2 CpG sites, but not other nearby sites, was negatively correlated with relative aromatase mRNA expression (R = - 0.52, P = 0.017 and R = - 0.52, P = 0.015). In contrast subcutaneous adipocytes percentage DNA methylation at the I.4.3 and I.4.5 sites were positively correlated with relative aromatase mRNA expression (R = 0.47, P = 0.022 and R = 0.55, P = 0.004). In a small subset of patients DNA methylation at the I.4.5 site was also positively correlated with whole body lean mass, bone mineral content and density.    Conclusions  In conclusion in mature adipocytes, the primary source of estradiol after menopause, increasing DNA methylation was correlated with aromatase mRNA expression and thus estradiol biosynthesis. These findings support a tissue-specific epigenetic regulation of the basal promoter activity in mature adipocytes; the mechanisms influencing this regulation and its physiological role remain to be elucidated.

DNA methylation within the I.4 promoter region correlates with CYPl19A1 gene expression in human ex vivo mature omental and subcutaneous adipocytes