Effect of folate deficiency on promoter methylation and gene expression of Esr1, Cdh1 and Pgr, and its influence on endometrial receptivity and embryo implantation.

BACKGROUND: Folate, one of the B vitamins, provides the one-carbon units required for methylation. Folate deficiency has been associated with many pathologies. However, much less is known about the effect of it on human reproduction, especially on implantation. The establishment of uterine receptivity is crucial for successful embryo implantation. Gene expression can be influenced by both heredity and epigenetics such as DNA methylation. However, it is not known whether the methylation and expression of genes related to uterine receptivity can be affected by folate levels. To explore whether folate deficiency affected the epigenetic regulation of genes related to uterine receptivity, and their influence on implantation, we investigated the methylation and expression of cadherin 1 (Cdh1), progesterone receptor (Pgr) and estrogen receptor 1 (Esr1) genes during implantation and the implantation efficiency using a folate-deficient pregnant mouse model.
METHODS: Serum folate levels of pregnant mice were measured using the electro-chemiluminescence immunoassay. The methylation status of Cdh1, Pgr and Esr1 promoter regions was determined by methylation-specific PCR and bisulfite sequencing. The expression of Cdh1, Pgr and Esr1 in the implantation-site endometrium was examined by real-time PCR, western blot and immunohistochemistry. The number and the morphology of pinopodes, important morphological markers of endometrial receptivity, were examined using scanning electron microscopy. The number of implantation sites demarcated by distinct blue bands was recorded.
RESULTS: Serum folate levels of the folate-deficient group were lower (5.42 ± 1.35 ng/ml, n= 42) than those of the normal group (24.13 ± 4 .26 ng/ml, n= 37; P = 0.003). Here we show that the methylation status and mRNA levels of Esr1 were decreased (P= 0.021, P= 0.045, respectively), while the Cdh1 and Pgr expression levels were slightly but not significantly elevated and the methylation status did not vary in the folate-deficient mice compared with the wild type. Neither the number nor morphology of pinopodes was affected by folate deficiency. Furthermore, folate deficiency did not affect the number of implantation sites in mice.
CONCLUSIONS: This study demonstrates for the first time that, unlike the effects on Esr1, folate deficiency in mice does not influence the methylation and expression of Pgr and Cdh1, two genes shown to be essential for uterine receptivity and embryo implantation. Embryo implantation in mice appears to be unaffected by a deficiency in folate, suggesting that abnormalities in a pregnancy caused by folate deficiency start to develop after implantation.