DNA methylation of the progesterone receptor B (PR-B) gene promoter in human eutopic endometrium, ectopic peritoneum, and ovarian endometriosis

Endometriosis, a chronic inflammatory disorder, is characterized by the presence of hormone-responsive, endometrial-like tissue outside of the uterine inner wall, such as in the peritoneum and ovaries. Progesterone (P) resistance, due to altered expression of progesterone receptor (PR), is known as a disruptive condition in response to P in eutopic endometrial tissue. Gene promoter DNA methylation, a gene silencing mechanism, has been associated with the etiology of endometriosis. The aim of this cross sectional study was to assess the DNA methylation status of the PR-B promoter in various tissues (eutopic endometrium, ectopic peritoneal, and ovarian lesions) from endometriosis patient. This study involved 20 samples for each tissue type (eutopic endometrium, peritoneal, and ovarian lesion from women with endometriosis), as compared with 20 eutopic microcurettage samplings of normal endometrial tissue. DNA was isolated from each sample and subjected to bisulfite conversion. The DNA methylation level of the PR-B gene promoter was analyzed by the methylation-specific PCR (MSP) method. Band intensities in agarose gels were measured with ImageJ software. The ratio of the band intensity of samples to that of the positive control was considered as the DNA methylation level. The Mann-Whitney U test and Wilcoxon test were conducted, and P-values were considered significant at < 0.05. There were significant differences in the methylation levels of the PR-B gene promoters in ectopic peritoneal endometrial tissue (72.40% methylated), ovarian tissue (85% methylated), and eutopic endometrial tissue (72.21% methylated), as compared to normal endometrium (P = 0.000). Moreover, there were no significant differences in methylation levels of the endometriosis samples, i.e., peritoneal vs. eutopic endometrial tissue, peritoneal vs. ovarian endometrial tissue, and ovarian vs. eutopic endometrial tissue (P = 0.636, 0.241, and 0.441, respectively). Hypermethylation of the PR-B gene promoter could cause P resistance in different types of endometriosis lesions and might be a potential biomarker for diagnosis of endometriosis.