GATA6 expression promoted by an active enhancer may become a molecular marker in endometriosis lesions

Problem Genome‐wide profiling of DNA methylation in endometriotic cells has shown a distinct facet of epigenetic backgrounds; however, specific DNA methylation sites responsible for aberrant gene expression in endometriosis were unknown. Are there specific endometriosis‐associated DNA methylations that can be used as molecular markers in endometriosis lesions? Method of study This study used endometriotic tissues from the chocolate cyst lining of the ovaries of patients with endometriosis, and endometrial tissues from disease‐free patients. For analysis, stromal cells were collected from endometrial and endometriotic tissues. Using endometrial cells as control, differentially methylated cytosine‐phosphate‐guanine (CpG) characteristic in endometriotic cells was extracted. Among these CpGs, we focused on a stretch of hypomethylated CpGs within GATA6 gene and examined the potential role as enhancer in endometriotic cells and tissues. Result(s) We identified a stretch of hypomethylated CpGs within the GATA6 gene body in endometriotic cells. Because GATA6 mRNA was highly expressed in endometriotic cells but not in endometrial cells, we then hypothesized that the hypomethylated sequence may function as an enhancer in GATA6 gene expression. Chromatin immunoprecipitation analysis predicted the presence of active enhancer within the gene body sequence in endometriotic cells. Immunohistochemistry showed a positive staining of GATA6 in ovarian chocolate cysts, while in endometrial tissues and in some peritoneal tissues with endometriosis, GATA6 staining was at a marginal level. Conclusion This is the first implication showing a link between an aberrant DNA methylation of cis element and gene expression in endometriosis. GATA6 expression may become a molecular marker to diagnose endometriosis lesions.