Background: Ten Eleven Translocation Proteins (TET) mediate DNA hydroxymethylation, a biologically critical epigenetic mechanism that is known to activate gene expression. Previously, our data demonstrated significant and dynamic changes in the mRNA expression of TETs across the menstrual cycle. The aim of this study is to localise TET proteins and determine the hormonal regulation of TETs in the endometrium.
Methods: Endometrial tissues were obtained after informed written consent from women with normal cycles. TETs were localised using colorimetric immunohistochemistry. To determine the hormonal regulation of TETs, HES cells (endometrial epithelial cell-line) were first treated with estradiol for 24hours and subsequently treated with a combination of estrogen and progesterone for 24, 48 and 72hours, in vitro. RNA was extracted and TET gene expression was determined using real-time PCR.
Results: TET proteins were localized in the nucleus of epithelial and stromal cells, throughout the menstrual cycle. Strong immunostaining of TET1 and 2 were observed in the glandular epithelium, during proliferative, early and mid-secretory phases which reduced during the late-secretory phase. Conversely, TET3 immunostaining was the highest during proliferative phase, then reduced during the mid to late-secretory phases. Strong universal staining was seen throughout the glandular and luminal epithelium. In contrast, staining in the stroma was not universal with immunostaining present in some cells and absent in others throughout the stroma. TET 1 and TET 3 transcriptions in HES cells were up-regulated in response to combined treatment of estrogen and progesterone for 72hours compared to control. While, TET2 transcription was the highest with the combined treatment for 48hours.
Conclusion: Our data imply that TETs are expressed in a cell-specific and dynamic manner in the endometrium and they are responsive to varying levels of estrogen and progesterone. Further investigations are underway to elucidate their role and interaction with other epigenetic machineries in the endometrium.