Peroxisome proliferator-activated receptor delta expression and regulation in mouse uterus during embryo implantation and decidualization.

The aim of this study was to examine the expression and regulation of peroxisome proliferator-activated receptor (PPAR) PPARdelta gene in mouse uterus during early pregnancy by in situ hybridization and immunohistochemistry. PPARdelta expression under pseudopregnancy, delayed implantation, hormonal treatment, and artificial decidualization was also investigated. There was a very low level of PPARdelta expression on days 1-4 of pregnancy. On day 5 when embryo implanted, PPARdelta expression was exclusively observed in the subluminal stroma surrounding the implanting blastocyst. No corresponding signals were seen in the uterus on day 5 of pregnancy. There was no detectable PPARdelta signal under delayed implantation. Once delayed implantation was terminated by estrogen treatment and embryo implanted, a strong level of PPARdelta expression was induced in the subluminal stroma surrounding the implanting blastocyst. Estrogen treatment induced a moderate level of PPARdelta expression in the glandular epithelium, while progesterone treatment had no effects in the ovariectomized mice. A strong level of PPARdelta expression was seen in the decidua on days 6-8 of pregnancy. PPARdelta expression was also induced under artificial decidualization. These data suggest that PPARdelta expression at implantation sites require the presence of an active blastocyst and may play an essential role for blastocyst implantation.