Background: The term DNA modification generally referred to the process where a methyl group is added to the cytosine to form 5-methylcytosine (5mC). However, recently, 5-hydroxymethylation (5hmc) has also been identified as a biologically critical epigenetic modification. The 5mC generated from DNA methylation down-regulates gene expression or leads to gene silencing whereas 5hmC, produced from DNA hydroxymethylation is known to perform alternative functions. Mediated by three Ten Eleven Translocation (TET) enzymes, the role of hydroxymethylation in the endometrium has not yet been explored. The aim of this study was to characterize TET1, 2 and 3 expression across the menstrual cycle and further, to determine the effect of steroid hormones on epithelial and stromal cells independently.
Methods: Endometrial tissue biopsies were collected from women of reproductive age with regular menstrual cycles. Endometrial epithelial (HES) and stromal (HESC) cell-lines were treated with either control, estradiol, progesterone or a combination of both. TET gene expression was determined using Real-time PCR.
Results: TET1 and TET3 mRNA expressions in the mid-secretory phase were significantly up-regulated compared to proliferative phase and the early secretory phase. TET1 and TET3 mRNA expressions were down-regulated in the late and early secretory phases, respectively. Preliminary data imply that estrogen up-regulated TET1 and TET3 mRNA in HESC cells post 48 hours of treatment. TET1, 2 and 3 mRNA expressions were down-regulated in HESC cells while in HES cells, TET3 mRNA was up-regulated in response to 48 hours of estrogen and progesterone treatment.
Conclusion: Our data imply that TET1, 2, 3 are dynamically expressed in the endometrium during the menstrual cycle. Furthermore, cell specific regulation of TET enzymes by the steroid hormones is also apparent. Further studies are underway to explore the relationship between DNA methylation and hydroxymethylation and their role in gene regulation in human endometrium.