Our previous whole genome expression analysis of endometriomas suggested
dysregulation of the ten-eleven translocation genes (TET1, TET2, and TET3), involved in converting 5-
methylcytosine to 5-hydroxymethylcytosine (5-hmC). The objective of this study was to validate the expression
of TET genes in ectopic and eutopic endometrium and in primary cultures of human endometrial stromal
fibroblasts (HESF) during in vitro decidualization and to quantify 5-hmC levels in patients with endometriosis.
Blood, eutopic endometrium, and endometriotic tissues were collected at time of gynecologic surgery. HESF
cultures were created from eutopic endometrium of women without (HESF-CONTROL) and with endometriosis
(HESF-ENDO) and underwent in vitro decidualization. Genomic DNA from blood and tissues underwent
quantification of the absolute amount of 5-hmC using ELISA. The expression of TET1, TET2, and TET3 was
decreased in endometriosis compared to non-endometriosis control eutopic endometrium. Surprisingly, the
global amount of 5-hmC was higher in ectopic endometrium than control eutopic endometrium, while genomic
DNA from blood of women with endometriosis contained statistically significantly less 5-hmC than women
without endometriosis. Expression of TET1, TET2, and TET3 was decreased in non-decidualized HESFENDO.
Upon in vitro decidualization, control HESF showed decreased expression of TET3, while decidualized
HESF-ENDO showed no statistically significant change in expression of TET1, TET2, or TET3. These results
indicate that the TET genes are downregulated in ectopic endometrium and in HESF-ENDO, and suggest for
the first time that TET genes play a role in endometriosis. High global amounts of 5-hmC in endometriotic
tissues suggest unique epigenetic regulation in these tissues.