Post-translational changes of histones, methylation level, and ERβ protein level in the cumulus cell genome of infertile women with endometriosis

Background: Endometriosis (which affects up to 50% of infertile women) is one of the major causes impacting female infertility. Endometriosis, defined as the presence of endometrial glands and stroma outside the uterine tissue, causes a wide range of functional disorders in the process of follicular development and changes in the follicular milieu, resulting in the formation of an incompetent oocyte to develop a high-quality embryo. This study was designed to obtain an overview of the epigenetic status of cumulus cells (as important ovarian cells that provide the physical support and microenvironment required for the developing oocyte) in endometriosis, quantitative evaluation of post-translational histone changes (acetylation and methylation of H3), total DNA methylation level, and the incorporation of estrogen receptor β protein (ERβ, as an important transcription factor in the process of disease pathogenesis) on the genome. Methods: This study was designed as a case-control study and cumulus cells were obtained from 12 infertile patients with endometriosis and 12 women with male factor infertility (as a control group) under ovulation stimulation protocols for intracytoplasmic sperm injection. Extraction of chromatin from cumulus cells was done after stabilization of DNA binding proteins and then cell lysis and preparation of soluble chromatin. The binding and incorporation levels of MeCP2 protein (as DNA methylation marker), two epigenetic markers related to histone modifications (H3K9me2 and H3K9ac), and ERβ protein to the chromatin of cumulus cells were evaluated using the corresponding primary antibodies, secondary antibodies conjugated and Nucleosome-ELISA technique. Results: MeCP2 protein incorporation was significantly higher in the endometriosis group than in the control group. The level of two epigenetic marks H3K9ac and H3K9me2 in the chromatin of cumulus cells of the patient group showed a significant increase compared to the control group (P<0.05). In addition, an increased level of binding of ERβ protein to the genome was observed compared to the control group. Discussion: Epigenetic changes, including histone hyperacetylation and hypermethylation and DNA hypermethylation of the whole genome of cumulus cells of patients with endometriosis have occurred along with an increase in the level of ERβ binding. These factors that cause changes in the level of gene expression possibly have a dynamic role in modifying the expression of genes in these patients' ovarian cells, causing abnormalities in the oocyte growth environment and subsequently the development of low-quality oocytes in these patients.