Novel role for conceptus signals in mRNA expression regulation by DNA methylation in porcine endometrium during early pregnancy

During early pregnancy, porcine conceptuses (the embryos with associated membranes) secrete estradiol-17 beta (E-2)-their major signal for maternal recognition of pregnancy-and prostaglandin E-2 (PGE(2)). Both hormones induce prominent changes of the endometrial transcriptome in vivo. Studies on endometrial pathologies have shown that E-2 affects gene expression by epigenetic mechanisms related to DNA methylation. Herein, we determined the effects of E-2 and PGE(2) alone, and a combined E-2 + PGE(2) treatment administered into the uterine lumen in vivo on the expression and activity of DNA-methyltransferases (DNMTs) and on CpG methylation patterns of selected genes in porcine endometrium. To compare the effect of treatment with the physiological effect of pregnancy, endometria from day 12 pregnant/cyclic gilts were included. Both E-2 and PGE(2) significantly reduced the expression of DNMTs. Likewise, the expressions of DNMT1 and DNMT3A were decreased on day 12 of pregnancy compared to the estrous cycle. DNMT activity increased in endometrial samples following E-2 treatment and in gilts on day 12 of pregnancy. Treatment with E-2 alone and/or simultaneously with PGE(2) altered endometrial DNA methylation of CpG sites of ADAMTS20, ADH1C, BGN, PSAT1, and WNT5A. Different CpG methylation patterns of ADAMTS20, BGN, DMBT1, RASSF1, and WNT5A were found in the endometrium on day 12 of pregnancy compared to day 12 of the estrous cycle. Significant correlations were detected between CpG methylation and gene expression for ADAMTS20, ADH1C, BGN, DMBT1, PSAT1, and WNT5A. Our results indicate that CpG methylation induced by embryonic signals may contribute to regulating endometrial gene expression during pregnancy establishment.