Background: In ovarian endometriomas (OE), the expression statuses of various steroid hormone receptors are altered compared with their expression statuses in eutopic endometrium (EE). For example, in OE, the expressions of estrogen receptor 1 (ESR1), which encodes ERα, and progesterone receptor (PGR) are downregulated, while the expression of ESR2, which encodes ERβ, is upregulated. The causes of these changes are unclear. DNA methylation of a specific region of a gene can result in tissue-specific gene expression. Such regions are called tissue-dependent and differentially methylated regions (T-DMRs). We previously reported that the tissue-specific expression of ESR1 is regulated by DNA methylation of a T-DMR in normal tissues. In the present study, we examined whether aberrant DNA methylation of the T-DMR is associated with the altered expressions of ESR1, ESR2 and PGR in OE.
Results: Gene expression levels of ESR1, ESR2 and PGR were measured by quantitative RT-PCR. The expression levels of ESR1 and PGR were significantly lower and the expression level of ESR2 was significantly higher in OE than in EE. DNA methylation statuses were examined with an Infinium HumanMethylation450K BeadChip and sodium bisulfite sequencing. DNA methylation at the T-DMRs of ESR1 were significantly higher in OE than in EE, but no significant differences were observed in the DNA methylation statuses of ESR2 and PGR.
Conclusions: Aberrant DNA methylation of the T-DMR was associated with the impaired expression of ESR1, but not the altered expressions of ESR2 and PGR, in OE.
Keywords: DNA methylation; Endometriosis; Estrogen receptor 1; Estrogen receptor 2; Eutopic endometrium; Ovarian endometrioma; Progesterone receptor; Steroid receptor.